// dear imgui: Renderer Backend for modern OpenGL with shaders / programmatic pipeline
// - Desktop GL: 2.x 3.x 4.x
// - Embedded GL: ES 2.0 (WebGL 1.0), ES 3.0 (WebGL 2.0)
// This needs to be used along with a Platform Backend (e.g. GLFW, SDL, Win32, custom..)

// Implemented features:
//  [X] Renderer: User texture binding. Use 'GLuint' OpenGL texture identifier as void*/ImTextureID. Read the FAQ about ImTextureID!
//  [x] Renderer: Large meshes support (64k+ vertices) with 16-bit indices (Desktop OpenGL only).

// About WebGL/ES:
// - You need to '#define IMGUI_IMPL_OPENGL_ES2' or '#define IMGUI_IMPL_OPENGL_ES3' to use WebGL or OpenGL ES.
// - This is done automatically on iOS, Android and Emscripten targets.
// - For other targets, the define needs to be visible from the imgui_impl_opengl3.cpp compilation unit. If unsure, define globally or in imconfig.h.

// You can use unmodified imgui_impl_* files in your project. See examples/ folder for examples of using this.
// Prefer including the entire imgui/ repository into your project (either as a copy or as a submodule), and only build the backends you need.
// Learn about Dear ImGui:
// - FAQ                  https://dearimgui.com/faq
// - Getting Started      https://dearimgui.com/getting-started
// - Documentation        https://dearimgui.com/docs (same as your local docs/ folder).
// - Introduction, links and more at the top of imgui.cpp

// CHANGELOG
// (minor and older changes stripped away, please see git history for details)
//  2024-05-07: OpenGL: Update loader for Linux to support EGL/GLVND. (#7562)
//  2024-04-16: OpenGL: Detect ES3 contexts on desktop based on version string, to e.g. avoid calling glPolygonMode() on them. (#7447)
//  2024-01-09: OpenGL: Update GL3W based imgui_impl_opengl3_loader.h to load "libGL.so" and variants, fixing regression on distros missing a symlink.
//  2023-11-08: OpenGL: Update GL3W based imgui_impl_opengl3_loader.h to load "libGL.so" instead of "libGL.so.1", accommodating for NetBSD systems having only "libGL.so.3" available. (#6983)
//  2023-10-05: OpenGL: Rename symbols in our internal loader so that LTO compilation with another copy of gl3w is possible. (#6875, #6668, #4445)
//  2023-06-20: OpenGL: Fixed erroneous use glGetIntegerv(GL_CONTEXT_PROFILE_MASK) on contexts lower than 3.2. (#6539, #6333)
//  2023-05-09: OpenGL: Support for glBindSampler() backup/restore on ES3. (#6375)
//  2023-04-18: OpenGL: Restore front and back polygon mode separately when supported by context. (#6333)
//  2023-03-23: OpenGL: Properly restoring "no shader program bound" if it was the case prior to running the rendering function. (#6267, #6220, #6224)
//  2023-03-15: OpenGL: Fixed GL loader crash when GL_VERSION returns NULL. (#6154, #4445, #3530)
//  2023-03-06: OpenGL: Fixed restoration of a potentially deleted OpenGL program, by calling glIsProgram(). (#6220, #6224)
//  2022-11-09: OpenGL: Reverted use of glBufferSubData(), too many corruptions issues + old issues seemingly can't be reproed with Intel drivers nowadays (revert 2021-12-15 and 2022-05-23 changes).
//  2022-10-11: Using 'nullptr' instead of 'NULL' as per our switch to C++11.
//  2022-09-27: OpenGL: Added ability to '#define IMGUI_IMPL_OPENGL_DEBUG'.
//  2022-05-23: OpenGL: Reworking 2021-12-15 "Using buffer orphaning" so it only happens on Intel GPU, seems to cause problems otherwise. (#4468, #4825, #4832, #5127).
//  2022-05-13: OpenGL: Fixed state corruption on OpenGL ES 2.0 due to not preserving GL_ELEMENT_ARRAY_BUFFER_BINDING and vertex attribute states.
//  2021-12-15: OpenGL: Using buffer orphaning + glBufferSubData(), seems to fix leaks with multi-viewports with some Intel HD drivers.
//  2021-08-23: OpenGL: Fixed ES 3.0 shader ("#version 300 es") use normal precision floats to avoid wobbly rendering at HD resolutions.
//  2021-08-19: OpenGL: Embed and use our own minimal GL loader (imgui_impl_opengl3_loader.h), removing requirement and support for third-party loader.
//  2021-06-29: Reorganized backend to pull data from a single structure to facilitate usage with multiple-contexts (all g_XXXX access changed to bd->XXXX).
//  2021-06-25: OpenGL: Use OES_vertex_array extension on Emscripten + backup/restore current state.
//  2021-06-21: OpenGL: Destroy individual vertex/fragment shader objects right after they are linked into the main shader.
//  2021-05-24: OpenGL: Access GL_CLIP_ORIGIN when "GL_ARB_clip_control" extension is detected, inside of just OpenGL 4.5 version.
//  2021-05-19: OpenGL: Replaced direct access to ImDrawCmd::TextureId with a call to ImDrawCmd::GetTexID(). (will become a requirement)
//  2021-04-06: OpenGL: Don't try to read GL_CLIP_ORIGIN unless we're OpenGL 4.5 or greater.
//  2021-02-18: OpenGL: Change blending equation to preserve alpha in output buffer.
//  2021-01-03: OpenGL: Backup, setup and restore GL_STENCIL_TEST state.
//  2020-10-23: OpenGL: Backup, setup and restore GL_PRIMITIVE_RESTART state.
//  2020-10-15: OpenGL: Use glGetString(GL_VERSION) instead of glGetIntegerv(GL_MAJOR_VERSION, ...) when the later returns zero (e.g. Desktop GL 2.x)
//  2020-09-17: OpenGL: Fix to avoid compiling/calling glBindSampler() on ES or pre 3.3 context which have the defines set by a loader.
//  2020-07-10: OpenGL: Added support for glad2 OpenGL loader.
//  2020-05-08: OpenGL: Made default GLSL version 150 (instead of 130) on OSX.
//  2020-04-21: OpenGL: Fixed handling of glClipControl(GL_UPPER_LEFT) by inverting projection matrix.
//  2020-04-12: OpenGL: Fixed context version check mistakenly testing for 4.0+ instead of 3.2+ to enable ImGuiBackendFlags_RendererHasVtxOffset.
//  2020-03-24: OpenGL: Added support for glbinding 2.x OpenGL loader.
//  2020-01-07: OpenGL: Added support for glbinding 3.x OpenGL loader.
//  2019-10-25: OpenGL: Using a combination of GL define and runtime GL version to decide whether to use glDrawElementsBaseVertex(). Fix building with pre-3.2 GL loaders.
//  2019-09-22: OpenGL: Detect default GL loader using __has_include compiler facility.
//  2019-09-16: OpenGL: Tweak initialization code to allow application calling ImGui_ImplOpenGL3_CreateFontsTexture() before the first NewFrame() call.
//  2019-05-29: OpenGL: Desktop GL only: Added support for large mesh (64K+ vertices), enable ImGuiBackendFlags_RendererHasVtxOffset flag.
//  2019-04-30: OpenGL: Added support for special ImDrawCallback_ResetRenderState callback to reset render state.
//  2019-03-29: OpenGL: Not calling glBindBuffer more than necessary in the render loop.
//  2019-03-15: OpenGL: Added a GL call + comments in ImGui_ImplOpenGL3_Init() to detect uninitialized GL function loaders early.
//  2019-03-03: OpenGL: Fix support for ES 2.0 (WebGL 1.0).
//  2019-02-20: OpenGL: Fix for OSX not supporting OpenGL 4.5, we don't try to read GL_CLIP_ORIGIN even if defined by the headers/loader.
//  2019-02-11: OpenGL: Projecting clipping rectangles correctly using draw_data->FramebufferScale to allow multi-viewports for retina display.
//  2019-02-01: OpenGL: Using GLSL 410 shaders for any version over 410 (e.g. 430, 450).
//  2018-11-30: Misc: Setting up io.BackendRendererName so it can be displayed in the About Window.
//  2018-11-13: OpenGL: Support for GL 4.5's glClipControl(GL_UPPER_LEFT) / GL_CLIP_ORIGIN.
//  2018-08-29: OpenGL: Added support for more OpenGL loaders: glew and glad, with comments indicative that any loader can be used.
//  2018-08-09: OpenGL: Default to OpenGL ES 3 on iOS and Android. GLSL version default to "#version 300 ES".
//  2018-07-30: OpenGL: Support for GLSL 300 ES and 410 core. Fixes for Emscripten compilation.
//  2018-07-10: OpenGL: Support for more GLSL versions (based on the GLSL version string). Added error output when shaders fail to compile/link.
//  2018-06-08: Misc: Extracted imgui_impl_opengl3.cpp/.h away from the old combined GLFW/SDL+OpenGL3 examples.
//  2018-06-08: OpenGL: Use draw_data->DisplayPos and draw_data->DisplaySize to setup projection matrix and clipping rectangle.
//  2018-05-25: OpenGL: Removed unnecessary backup/restore of GL_ELEMENT_ARRAY_BUFFER_BINDING since this is part of the VAO state.
//  2018-05-14: OpenGL: Making the call to glBindSampler() optional so 3.2 context won't fail if the function is a nullptr pointer.
//  2018-03-06: OpenGL: Added const char* glsl_version parameter to ImGui_ImplOpenGL3_Init() so user can override the GLSL version e.g. "#version 150".
//  2018-02-23: OpenGL: Create the VAO in the render function so the setup can more easily be used with multiple shared GL context.
//  2018-02-16: Misc: Obsoleted the io.RenderDrawListsFn callback and exposed ImGui_ImplSdlGL3_RenderDrawData() in the .h file so you can call it yourself.
//  2018-01-07: OpenGL: Changed GLSL shader version from 330 to 150.
//  2017-09-01: OpenGL: Save and restore current bound sampler. Save and restore current polygon mode.
//  2017-05-01: OpenGL: Fixed save and restore of current blend func state.
//  2017-05-01: OpenGL: Fixed save and restore of current GL_ACTIVE_TEXTURE.
//  2016-09-05: OpenGL: Fixed save and restore of current scissor rectangle.
//  2016-07-29: OpenGL: Explicitly setting GL_UNPACK_ROW_LENGTH to reduce issues because SDL changes it. (#752)

//----------------------------------------
// OpenGL    GLSL      GLSL
// version   version   string
//----------------------------------------
//  2.0       110       "#version 110"
//  2.1       120       "#version 120"
//  3.0       130       "#version 130"
//  3.1       140       "#version 140"
//  3.2       150       "#version 150"
//  3.3       330       "#version 330 core"
//  4.0       400       "#version 400 core"
//  4.1       410       "#version 410 core"
//  4.2       420       "#version 410 core"
//  4.3       430       "#version 430 core"
//  ES 2.0    100       "#version 100"      = WebGL 1.0
//  ES 3.0    300       "#version 300 es"   = WebGL 2.0
//----------------------------------------

// Configuration flags to add in your imconfig file:
//IMGUI_IMPL_OPENGL_ES2 :: 1;     // Enable ES 2 (Auto-detected on Emscripten)
//IMGUI_IMPL_OPENGL_ES3 :: 1;     // Enable ES 3 (Auto-detected on iOS/Android)

// You can explicitly select GLES2 or GLES3 API by using one of the
// '#define IMGUI_IMPL_OPENGL_LOADER_XXX' in imconfig.h or compiler command-line.
#if !#exists(IMGUI_IMPL_OPENGL_ES2) && !#exists(IMGUI_IMPL_OPENGL_ES3) {

    // Try to detect GLES on matching platforms
    #if OS == .MACOS {
        //#include <TargetConditionals.h>
        //#assert false "Please include the platform header TargetConditionals.h somehow.";
    }
    #if OS == .MACOS && (#exists(TARGET_OS_IOS) || #exists(TARGET_OS_TV)) || #exists(__ANDROID__) {
        IMGUI_IMPL_OPENGL_ES3 :: 1;               // iOS, Android  -> GL ES 3, "#version 300 es"
    } else #if #exists(__EMSCRIPTEN__) || #exists(__amigaos4__) {
        IMGUI_IMPL_OPENGL_ES2 :: 1;               // Emscripten    -> GL ES 2, "#version 100"
    } else {
        // Otherwise imgui_impl_opengl3_loader.h will be used.
    }
}

// GL includes
#if #exists(IMGUI_IMPL_OPENGL_ES2) {
    #if OS == .MACOS && (#exists(TARGET_OS_IOS) || #exists(TARGET_OS_TV)) {
        //#include <OpenGLES/ES2/gl.h>    // Use GL ES 2
        #assert false "Please include the platform header OpenGLES/ES2/gl.h somehow.";
    } else {
        //#include <GLES2/gl2.h>          // Use GL ES 2
        #assert false "Please include the platform header GLES2/gl2.h somehow.";
    }
    #if #exists(__EMSCRIPTEN__) {
        #if !#exists(GL_GLEXT_PROTOTYPES) {
            GL_GLEXT_PROTOTYPES :: 1;
        }
        //#include <GLES2/gl2ext.h>
        #assert false "Please include the platform header GLES2/gl2ext.h somehow.";
    }
} else #if #exists(IMGUI_IMPL_OPENGL_ES3) {
    #if #exists(__APPLE__) && (#exists(TARGET_OS_IOS) || #exists(TARGET_OS_TV)) {
        //#include <OpenGLES/ES3/gl.h>    // Use GL ES 3
        #assert false "Please include the platform header OpenGLES/ES3/gl.h somehow.";
    } else {
        //#include <GLES3/gl3.h>          // Use GL ES 3
        #assert false "Please include the platform header GLES3/gl3.h somehow.";
    }
} else #if !#exists(IMGUI_IMPL_OPENGL_LOADER_CUSTOM) {
    // Modern desktop OpenGL doesn't have a standard portable header file to load OpenGL function pointers.
    // Helper libraries are often used for this purpose! Here we are using our own minimal custom loader based on gl3w.
    // In the rest of your app/engine, you can use another loader of your choice (gl3w, glew, glad, glbinding, glext,
    //   glLoadGen, etc.).
    // If you happen to be developing a new feature for this backend (imgui_impl_opengl3.cpp):
    // - You may need to regenerate imgui_impl_opengl3_loader.h to add new symbols.
    //   See https://github.com/dearimgui/gl3w_stripped
    // - You can temporarily use an unstripped version. See https://github.com/dearimgui/gl3w_stripped/releases
    // Changes to this backend using new APIs should be accompanied by a regenerated stripped loader version.
    IMGL3W_IMPL :: 1;
    //#include "imgui_impl_opengl3_loader.h"
    // You're probably already doing #import "GL"; in your main program.
}

// Vertex arrays are not supported on ES2/WebGL1 unless Emscripten which uses an extension
#if !#exists(IMGUI_IMPL_OPENGL_ES2) {
    IMGUI_IMPL_OPENGL_USE_VERTEX_ARRAY :: 1;
} else #if #exists(__EMSCRIPTEN__) {
    IMGUI_IMPL_OPENGL_USE_VERTEX_ARRAY :: 1;
    glBindVertexArray       :: glBindVertexArrayOES;
    glGenVertexArrays       :: glGenVertexArraysOES;
    glDeleteVertexArrays    :: glDeleteVertexArraysOES;
    GL_VERTEX_ARRAY_BINDING :: GL_VERTEX_ARRAY_BINDING_OES;
}

// Desktop GL 2.0+ has extension and glPolygonMode() which GL ES and WebGL don't have..
// A desktop ES context can technically compile fine with our loader, so we also perform a runtime checks
#if !#exists(IMGUI_IMPL_OPENGL_ES2) && !#exists(IMGUI_IMPL_OPENGL_ES3) {
    IMGUI_IMPL_OPENGL_HAS_EXTENSIONS :: 1;        // has glGetIntegerv(GL_NUM_EXTENSIONS)
    IMGUI_IMPL_OPENGL_MAY_HAVE_POLYGON_MODE :: 1; // may have glPolygonMode()
}

// Desktop GL 2.1+ and GL ES 3.0+ have glBindBuffer() with GL_PIXEL_UNPACK_BUFFER target.
#if !#exists(IMGUI_IMPL_OPENGL_ES2) {
    IMGUI_IMPL_OPENGL_MAY_HAVE_BIND_BUFFER_PIXEL_UNPACK :: 1;
}

// Desktop GL 3.1+ has GL_PRIMITIVE_RESTART state
#if !#exists(IMGUI_IMPL_OPENGL_ES2) && !#exists(IMGUI_IMPL_OPENGL_ES3) && #exists(GL_VERSION_3_1) {
    IMGUI_IMPL_OPENGL_MAY_HAVE_PRIMITIVE_RESTART :: 1;
}

// Desktop GL 3.2+ has glDrawElementsBaseVertex() which GL ES and WebGL don't have.
#if !#exists(IMGUI_IMPL_OPENGL_ES2) && !#exists(IMGUI_IMPL_OPENGL_ES3) && #exists(GL_VERSION_3_2) {
    IMGUI_IMPL_OPENGL_MAY_HAVE_VTX_OFFSET :: 1;
}

// Desktop GL 3.3+ and GL ES 3.0+ have glBindSampler()
#if !#exists(IMGUI_IMPL_OPENGL_ES2) && (#exists(IMGUI_IMPL_OPENGL_ES3) || #exists(GL_VERSION_3_3)) {
    IMGUI_IMPL_OPENGL_MAY_HAVE_BIND_SAMPLER :: 1;
}

ImGui_ImplOpenGL3_Data :: struct {
    GlVersion : GLuint;               // Extracted at runtime using GL_MAJOR_VERSION, GL_MINOR_VERSION queries (e.g. 320 for GL 3.2)
    GlslVersionString : [32] u8;   // Specified by user or detected based on compile time GL settings.
    GlProfileIsES2 : bool;
    GlProfileIsES3 : bool;
    GlProfileIsCompat : bool;
    GlProfileMask : GLint;
    FontTexture : GLuint;
    ShaderHandle : GLuint;
    AttribLocationTex : GLint;       // Uniforms location
    AttribLocationProjMtx : GLint;
    AttribLocationVtxPos : GLuint;    // Vertex attributes location
    AttribLocationVtxUV : GLuint;
    AttribLocationVtxColor : GLuint;
    VboHandle, ElementsHandle : u32;
    VertexBufferSize : GLsizeiptr;
    IndexBufferSize : GLsizeiptr;
    HasPolygonMode : bool;
    HasClipOrigin : bool;
    UseBufferSubData : bool;
}

// Backend data stored in io.BackendRendererUserData to allow support for multiple Dear ImGui contexts
// It is STRONGLY preferred that you use docking branch with multi-viewports (== single Dear ImGui context + multiple windows) instead of multiple Dear ImGui contexts.
ImGui_ImplOpenGL3_GetBackendData :: () -> *ImGui_ImplOpenGL3_Data {
    return ifx ImGui.GetCurrentContext() then cast(*ImGui_ImplOpenGL3_Data) ImGui.GetIO().BackendRendererUserData else null;
}

// OpenGL vertex attribute state (for ES 1.0 and ES 2.0 only)
//#if !IMGUI_IMPL_OPENGL_USE_VERTEX_ARRAY {
ImGui_ImplOpenGL3_VtxAttribState :: struct {
    enabled, Size, Type, Normalized, Stride : GLint;
    Ptr : *void;
}

GetState :: (using state: *ImGui_ImplOpenGL3_VtxAttribState, index: GLint) {
    glGetVertexAttribiv(xx index, GL_VERTEX_ATTRIB_ARRAY_ENABLED, *enabled);
    glGetVertexAttribiv(xx index, GL_VERTEX_ATTRIB_ARRAY_SIZE, *Size);
    glGetVertexAttribiv(xx index, GL_VERTEX_ATTRIB_ARRAY_TYPE, *Type);
    glGetVertexAttribiv(xx index, GL_VERTEX_ATTRIB_ARRAY_NORMALIZED, *Normalized);
    glGetVertexAttribiv(xx index, GL_VERTEX_ATTRIB_ARRAY_STRIDE, *Stride);
    glGetVertexAttribPointerv(xx index, GL_VERTEX_ATTRIB_ARRAY_POINTER, *Ptr);
}

SetState :: (using state: *ImGui_ImplOpenGL3_VtxAttribState, index: GLint) {
    glVertexAttribPointer(xx index, Size, xx Type, cast(GLboolean) Normalized, xx Stride, Ptr);
    if enabled {
        glEnableVertexAttribArray(xx index);
    } else {
        glDisableVertexAttribArray(xx index);
    }
}
//}

// Functions
ImGui_ImplOpenGL3_Init :: (glsl_version: *string) -> bool {
    io : *ImGui.IO= ImGui.GetIO();
    ImGui.IMGUI_CHECKVERSION();
    assert(io.BackendRendererUserData == null && "Already initialized a renderer backend!");

    // Initialize our loader
//#if !#exists(IMGUI_IMPL_OPENGL_ES2) && !#exists(IMGUI_IMPL_OPENGL_ES3) && !#exists(IMGUI_IMPL_OPENGL_LOADER_CUSTOM) {
//    if imgl3wInit() != 0 {
//        log("Failed to initialize OpenGL loader!\n");
//        return false;
//    }
//}

    // Setup backend capabilities flags
    bd : *ImGui_ImplOpenGL3_Data = New(ImGui_ImplOpenGL3_Data);
    io.BackendRendererUserData = cast(*void) bd;
    io.BackendRendererName = "imgui_impl_opengl3";

    // Query for GL version (e.g. 320 for GL 3.2)
#if #exists(IMGUI_IMPL_OPENGL_ES2) {
    // GLES 2
    bd.GlVersion = 200;
    bd.GlProfileIsES2 = true;
} else {
    // Desktop or GLES 3
    gl_version_str : string = to_string(glGetString(GL_VERSION));
    major : GLint = 0;
    minor : GLint = 0;
    glGetIntegerv(GL_MAJOR_VERSION, *major);
    glGetIntegerv(GL_MINOR_VERSION, *minor);
    if major == 0 && minor == 0 {
        matched, items := scan("%i.%i", gl_version_str);
        for items
            print_vars(it);
    }

        // Query GL_VERSION in desktop GL 2.x, the string will start with "<major>.<minor>"
    bd.GlVersion = cast(GLuint) (major * 100 + minor * 10);
#if GL_CONTEXT_PROFILE_MASK {
    if (bd.GlVersion >= 320)
        glGetIntegerv(GL_CONTEXT_PROFILE_MASK, *bd.GlProfileMask);
    bd.GlProfileIsCompat = (bd.GlProfileMask & GL_CONTEXT_COMPATIBILITY_PROFILE_BIT) != 0;
}

#if #exists(IMGUI_IMPL_OPENGL_ES3) {
    bd.GlProfileIsES3 = true;
} else {
    if compare(gl_version_str, "OpenGL ES 3") == 0
        bd.GlProfileIsES3 = true;
}

    bd.UseBufferSubData = false;
    /*
    // Query vendor to enable glBufferSubData kludge
#ifdef _WIN32
    if (const char* vendor = (const char*)glGetString(GL_VENDOR))
        if (strncmp(vendor, "Intel", 5) == 0)
            bd->UseBufferSubData = true;
#endif
    */
}

#if #exists(IMGUI_IMPL_OPENGL_DEBUG) {
    print("GlVersion = %d, \"%s\"\nGlProfileIsCompat = %d\nGlProfileMask = 0x%X\nGlProfileIsES2 = %d, GlProfileIsES3 = %d\nGL_VENDOR = '%s'\nGL_RENDERER = '%s'\n", bd.GlVersion, gl_version_str, bd.GlProfileIsCompat, bd.GlProfileMask, bd.GlProfileIsES2, bd.GlProfileIsES3, cast(string) glGetString(GL_VENDOR), cast(string) glGetString(GL_RENDERER)); // [DEBUG]
}

#if #exists(IMGUI_IMPL_OPENGL_MAY_HAVE_VTX_OFFSET) {
    if bd.GlVersion >= 320
        io.BackendFlags_ |= ImGui.BackendFlags.RendererHasVtxOffset;
        // We can honor the ImDrawCmd::VtxOffset field, allowing for large meshes.
}

    // Store GLSL version string so we can refer to it later in case we recreate shaders.
    // Note: GLSL version is NOT the same as GL version. Leave this to nullptr if unsure.
    if glsl_version.data == null {
#if #exists(IMGUI_IMPL_OPENGL_ES2) {
        glsl_version.* = "#version 100";
} else #if #exists(IMGUI_IMPL_OPENGL_ES3) {
        glsl_version.* = "#version 300 es";
} else #if #exists(__APPLE__) {
        glsl_version.* = "#version 150";
} else {
        glsl_version.* = "#version 130";
}
    }
    assert(cast(s32) c_style_strlen(glsl_version.data) + 2 < size_of(type_of(bd.GlslVersionString)));
    memcpy(bd.GlslVersionString.data, glsl_version.data, c_style_strlen(glsl_version.data));
    bd.GlslVersionString[c_style_strlen(glsl_version.data)] = #char "\n";

    // Make an arbitrary GL call (we don't actually need the result)
    // IF YOU GET A CRASH HERE: it probably means the OpenGL function loader didn't do its job. Let us know!
    current_texture : GLint;
    glGetIntegerv(GL_TEXTURE_BINDING_2D, *current_texture);

    // Detect extensions we support
#if #exists(IMGUI_IMPL_OPENGL_MAY_HAVE_POLYGON_MODE) {
    bd.HasPolygonMode = (!bd.GlProfileIsES2 && !bd.GlProfileIsES3);
}
    bd.HasClipOrigin = (bd.GlVersion >= 450);
#if #exists(IMGUI_IMPL_OPENGL_HAS_EXTENSIONS) {
    num_extensions : GLint = 0;
    glGetIntegerv(GL_NUM_EXTENSIONS, *num_extensions);
    for i : 0..num_extensions -1 {
        extension : string = to_string(glGetStringi(GL_EXTENSIONS, xx i));
        if compare(extension, "GL_ARB_clip_control") == 0
            bd.HasClipOrigin = true;
    }
}

    return true;
}

ImGui_ImplOpenGL3_Shutdown :: () {
    bd : *ImGui_ImplOpenGL3_Data = ImGui_ImplOpenGL3_GetBackendData();
    assert(bd != null && "No renderer backend to shutdown, or already shutdown?");
    io : *ImGui.IO= ImGui.GetIO();

    ImGui_ImplOpenGL3_DestroyDeviceObjects();
    io.BackendRendererName = null;
    io.BackendRendererUserData = null;
    io.BackendFlags_ &= ~ImGui.BackendFlags.RendererHasVtxOffset;
    free(bd);
}

ImGui_ImplOpenGL3_NewFrame :: () {
    bd : *ImGui_ImplOpenGL3_Data = ImGui_ImplOpenGL3_GetBackendData();
    assert(bd != null && "Context or backend not initialized! Did you call ImGui_ImplOpenGL3_Init()?");

    if !bd.ShaderHandle
        ImGui_ImplOpenGL3_CreateDeviceObjects();
}

ImGui_ImplOpenGL3_SetupRenderState :: (draw_data : *ImGui.ImDrawData, fb_width : s32, fb_height : s32,
                                       vertex_array_object : GLuint) {
    bd : *ImGui_ImplOpenGL3_Data = ImGui_ImplOpenGL3_GetBackendData();

    // Setup render state: alpha-blending enabled, no face culling, no depth testing, scissor enabled, polygon fill
    glEnable(GL_BLEND);
    glBlendEquation(GL_FUNC_ADD);
    glBlendFuncSeparate(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA, GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
    glDisable(GL_CULL_FACE);
    glDisable(GL_DEPTH_TEST);
    glDisable(GL_STENCIL_TEST);
    glEnable(GL_SCISSOR_TEST);
#if #exists(IMGUI_IMPL_OPENGL_MAY_HAVE_PRIMITIVE_RESTART) {
    if bd.GlVersion >= 310
        glDisable(GL_PRIMITIVE_RESTART);
}
#if #exists(IMGUI_IMPL_OPENGL_MAY_HAVE_POLYGON_MODE) {
    if (bd.HasPolygonMode)
        glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
}

    // Support for GL 4.5 rarely used glClipControl(GL_UPPER_LEFT)
#if GL_CLIP_ORIGIN {
    clip_origin_lower_left : bool = true;
    if bd.HasClipOrigin {
        current_clip_origin : GLenum = 0;
        glGetIntegerv(GL_CLIP_ORIGIN, cast(*GLint) *current_clip_origin);
        if current_clip_origin == GL_UPPER_LEFT
            clip_origin_lower_left = false;
    }
}

    // Setup viewport, orthographic projection matrix
    // Our visible imgui space lies from draw_data->DisplayPos (top left) to draw_data->DisplayPos+data_data->DisplaySize (bottom right). DisplayPos is (0,0) for single viewport apps.
    glViewport(0, 0, cast(GLsizei) fb_width, cast(GLsizei) fb_height);
    L : float = draw_data.DisplayPos.x;
    R : float = draw_data.DisplayPos.x + draw_data.DisplaySize.x;
    T : float = draw_data.DisplayPos.y;
    B : float = draw_data.DisplayPos.y + draw_data.DisplaySize.y;
#if GL_CLIP_ORIGIN {
    if (!clip_origin_lower_left) {
        tmp : float = T;
        T = B;
        B = tmp;
    } // Swap top and bottom if origin is upper left
}
ortho_projection : [4][4] float = .[
        .[ 2.0/(R-L),   0.0,         0.0,   0.0 ],
        .[ 0.0,         2.0/(T-B),   0.0,   0.0 ],
        .[ 0.0,         0.0,        -1.0,   0.0 ],
        .[ (R+L)/(L-R),  (T+B)/(B-T),  0.0,   1.0 ],
    ];
    glUseProgram(bd.ShaderHandle);
    glUniform1i(bd.AttribLocationTex, 0);
    glUniformMatrix4fv(bd.AttribLocationProjMtx, 1, GL_FALSE, *ortho_projection[0][0]);

#if #exists(IMGUI_IMPL_OPENGL_MAY_HAVE_BIND_SAMPLER) {
    if bd.GlVersion >= 330 || bd.GlProfileIsES3
        glBindSampler(0, 0);
        // We use combined texture/sampler state. Applications using GL 3.3 and GL ES 3.0 may set that otherwise.
}

    //(void)vertex_array_object;
#if #exists(IMGUI_IMPL_OPENGL_USE_VERTEX_ARRAY) {
    glBindVertexArray(vertex_array_object);
}

    // Bind vertex/index buffers and setup attributes for ImDrawVert
    glBindBuffer(GL_ARRAY_BUFFER, bd.VboHandle);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, bd.ElementsHandle);
    glEnableVertexAttribArray(bd.AttribLocationVtxPos);
    glEnableVertexAttribArray(bd.AttribLocationVtxUV);
    glEnableVertexAttribArray(bd.AttribLocationVtxColor);
    glVertexAttribPointer(bd.AttribLocationVtxPos, 2, GL_FLOAT, GL_FALSE, size_of(ImGui.ImDrawVert),
                          cast(*GLvoid) offset_of(ImGui.ImDrawVert, #code pos));
    glVertexAttribPointer(bd.AttribLocationVtxUV, 2, GL_FLOAT, GL_FALSE, size_of(ImGui.ImDrawVert),
                          cast(*GLvoid) offset_of(ImGui.ImDrawVert, #code uv));
    glVertexAttribPointer(bd.AttribLocationVtxColor, 4, GL_UNSIGNED_BYTE, GL_TRUE, size_of(ImGui.ImDrawVert),
                          cast(*GLvoid) offset_of(ImGui.ImDrawVert, #code col));
}

// OpenGL3 Render function.
// Note that this implementation is little overcomplicated because we are saving/setting up/restoring every OpenGL state explicitly.
// This is in order to be able to run within an OpenGL engine that doesn't do so.
ImGui_ImplOpenGL3_RenderDrawData :: (draw_data: *ImGui.ImDrawData) {
    // Avoid rendering when minimized, scale coordinates for retina displays (screen coordinates != framebuffer coordinates)
    fb_width_f := (draw_data.DisplaySize.x * draw_data.FramebufferScale.x);
    fb_height_f := (draw_data.DisplaySize.y * draw_data.FramebufferScale.y);

    fb_width := cast(s32) fb_width_f;
    fb_height := cast(s32) fb_height_f;

    if fb_width <= 0 || fb_height <= 0
        return;

    bd: *ImGui_ImplOpenGL3_Data = ImGui_ImplOpenGL3_GetBackendData();

    // Backup GL state
    last_active_texture : GLenum;
    glGetIntegerv(GL_ACTIVE_TEXTURE, cast(*GLint) *last_active_texture);
    glActiveTexture(GL_TEXTURE0);
    last_program : GLuint;
    glGetIntegerv(GL_CURRENT_PROGRAM, cast(*GLint) *last_program);
    last_texture : GLuint;
    glGetIntegerv(GL_TEXTURE_BINDING_2D, cast(*GLint) *last_texture);

#if #exists(IMGUI_IMPL_OPENGL_MAY_HAVE_BIND_SAMPLER) {
    last_sampler : GLuint;
    if bd.GlVersion >= 330 || bd.GlProfileIsES3 {
        glGetIntegerv(GL_SAMPLER_BINDING, cast(*GLint) *last_sampler);
    } else {
        last_sampler = 0;
    }
}

    last_array_buffer : GLuint;
    glGetIntegerv(GL_ARRAY_BUFFER_BINDING, cast(*GLint) *last_array_buffer);

#if !#exists(IMGUI_IMPL_OPENGL_USE_VERTEX_ARRAY) {
    // This is part of VAO on OpenGL 3.0+ and OpenGL ES 3.0+.
    last_element_array_buffer : GLint;
    glGetIntegerv(GL_ELEMENT_ARRAY_BUFFER_BINDING, *last_element_array_buffer);
    last_vtx_attrib_state_pos : ImGui_ImplOpenGL3_VtxAttribState;
    GetState(*last_vtx_attrib_state_pos, xx bd.AttribLocationVtxPos);

    last_vtx_attrib_state_uv : ImGui_ImplOpenGL3_VtxAttribState;
    GetState(*last_vtx_attrib_state_uv, xx bd.AttribLocationVtxUV);

    last_vtx_attrib_state_color : ImGui_ImplOpenGL3_VtxAttribState;
    GetState(*last_vtx_attrib_state_color, xx bd.AttribLocationVtxColor);
}
#if #exists(IMGUI_IMPL_OPENGL_USE_VERTEX_ARRAY) {
    last_vertex_array_object : GLuint;
    glGetIntegerv(GL_VERTEX_ARRAY_BINDING, cast(*GLint) *last_vertex_array_object);
}

#if #exists(IMGUI_IMPL_OPENGL_MAY_HAVE_POLYGON_MODE) {
    last_polygon_mode : [2] GLint;
    if (bd.HasPolygonMode) {
        glGetIntegerv(GL_POLYGON_MODE, last_polygon_mode.data);
    }
}
    last_viewport : [4] GLint;
    glGetIntegerv(GL_VIEWPORT, last_viewport.data);
    last_scissor_box : [4]GLint;
    glGetIntegerv(GL_SCISSOR_BOX, last_scissor_box.data);
    last_blend_src_rgb : GLenum;
    glGetIntegerv(GL_BLEND_SRC_RGB, cast(*GLint) *last_blend_src_rgb);
    last_blend_dst_rgb : GLenum;
    glGetIntegerv(GL_BLEND_DST_RGB, cast(*GLint) *last_blend_dst_rgb);
    last_blend_src_alpha : GLenum;
    glGetIntegerv(GL_BLEND_SRC_ALPHA, cast(*GLint) *last_blend_src_alpha);
    last_blend_dst_alpha : GLenum;
    glGetIntegerv(GL_BLEND_DST_ALPHA, cast(*GLint) *last_blend_dst_alpha);
    last_blend_equation_rgb : GLenum;
    glGetIntegerv(GL_BLEND_EQUATION_RGB, cast(*GLint) *last_blend_equation_rgb);
    last_blend_equation_alpha : GLenum;
    glGetIntegerv(GL_BLEND_EQUATION_ALPHA, cast(*GLint) *last_blend_equation_alpha);

    last_enable_blend : GLboolean = glIsEnabled(GL_BLEND);
    last_enable_cull_face : GLboolean = glIsEnabled(GL_CULL_FACE);
    last_enable_depth_test : GLboolean = glIsEnabled(GL_DEPTH_TEST);
    last_enable_stencil_test : GLboolean = glIsEnabled(GL_STENCIL_TEST);
    last_enable_scissor_test : GLboolean = glIsEnabled(GL_SCISSOR_TEST);
#if #exists (IMGUI_IMPL_OPENGL_MAY_HAVE_PRIMITIVE_RESTART) {
    last_enable_primitive_restart : GLboolean = ifx (bd.GlVersion >= 310) then glIsEnabled(GL_PRIMITIVE_RESTART) else GL_FALSE;
}

    // Setup desired GL state
    // Recreate the VAO every time (this is to easily allow multiple GL contexts to be rendered to. VAO are not shared among GL contexts)
    // The renderer would actually work without any VAO bound, but then our VertexAttrib calls would overwrite the default one currently bound.
    vertex_array_object : GLuint = 0;
#if #exists(IMGUI_IMPL_OPENGL_USE_VERTEX_ARRAY) {
    glGenVertexArrays(1, *vertex_array_object);
}
    ImGui_ImplOpenGL3_SetupRenderState(draw_data, fb_width, fb_height, vertex_array_object);

    // Will project scissor/clipping rectangles into framebuffer space
    clip_off : ImGui.ImVec2 = draw_data.DisplayPos;         // (0,0) unless using multi-viewports
    clip_scale : ImGui.ImVec2 = draw_data.FramebufferScale; // (1,1) unless using retina display which are often (2,2)

    // Render command lists
    for n: 0..draw_data.CmdListsCount - 1 {
        cmd_list : *ImGui.ImDrawList = draw_data.CmdLists.Data[n];

        // Upload vertex/index buffers
        // - OpenGL drivers are in a very sorry state nowadays....
        //   During 2021 we attempted to switch from glBufferData() to orphaning+glBufferSubData() following reports
        //   of leaks on Intel GPU when using multi-viewports on Windows.
        // - After this we kept hearing of various display corruptions issues. We started disabling on non-Intel GPU, but issues still got reported on Intel.
        // - We are now back to using exclusively glBufferData(). So bd->UseBufferSubData IS ALWAYS FALSE in this code.
        //   We are keeping the old code path for a while in case people finding new issues may want to test the bd->UseBufferSubData path.
        // - See https://github.com/ocornut/imgui/issues/4468 and please report any corruption issues.
        vtx_buffer_size : GLsizeiptr = cast(GLsizeiptr) cmd_list.VtxBuffer.Size * cast(s32) size_of(ImGui.ImDrawVert);
        idx_buffer_size : GLsizeiptr = cast(GLsizeiptr) cmd_list.IdxBuffer.Size * cast(s32) size_of(ImGui.ImDrawIdx);
        if bd.UseBufferSubData {
            if bd.VertexBufferSize < vtx_buffer_size {
                bd.VertexBufferSize = vtx_buffer_size;
                glBufferData(GL_ARRAY_BUFFER, bd.VertexBufferSize, null, GL_STREAM_DRAW);
            }

            if bd.IndexBufferSize < idx_buffer_size {
                bd.IndexBufferSize = idx_buffer_size;
                glBufferData(GL_ELEMENT_ARRAY_BUFFER, bd.IndexBufferSize, null, GL_STREAM_DRAW);
            }
            glBufferSubData(GL_ARRAY_BUFFER, 0, vtx_buffer_size, cast(*GLvoid) cmd_list.VtxBuffer.Data);
            glBufferSubData(GL_ELEMENT_ARRAY_BUFFER, 0, idx_buffer_size, cast(*GLvoid) cmd_list.IdxBuffer.Data);
        } else {
            glBufferData(GL_ARRAY_BUFFER, vtx_buffer_size, cast(*GLvoid) cmd_list.VtxBuffer.Data, GL_STREAM_DRAW);
            glBufferData(GL_ELEMENT_ARRAY_BUFFER, idx_buffer_size, cast(*GLvoid) cmd_list.IdxBuffer.Data, GL_STREAM_DRAW);
        }

        for cmd_i: 0..cmd_list.CmdBuffer.Size {
            pcmd : *ImGui.ImDrawCmd = *cmd_list.CmdBuffer.Data[cmd_i];
            if pcmd.UserCallback != null {
                // User callback, registered via ImDrawList::AddCallback()
                // (ImDrawCallback_ResetRenderState is a special callback value used by the user to request the renderer to reset render state.)
                //if pcmd.UserCallback == ImDrawCallback_ResetRenderState {
                  //  ImGui_ImplOpenGL3_SetupRenderState(draw_data, fb_width, fb_height, vertex_array_object);
                //} else {
                    pcmd.UserCallback(cmd_list, pcmd);
                //}
            } else {
                // Project scissor/clipping rectangles into framebuffer space
                clip_min : ImGui.ImVec2 = .{(pcmd.ClipRect.x - clip_off.x) * clip_scale.x,
                                            (pcmd.ClipRect.y - clip_off.y) * clip_scale.y};
                clip_max : ImGui.ImVec2 = .{(pcmd.ClipRect.z - clip_off.x) * clip_scale.x,
                                            (pcmd.ClipRect.w - clip_off.y) * clip_scale.y};
                if clip_max.x <= clip_min.x || clip_max.y <= clip_min.y
                    continue;

                // Apply scissor/clipping rectangle (Y is inverted in OpenGL)
                glScissor(xx cast(s32)clip_min.x, xx cast(s32)(cast(float) fb_height - clip_max.y),
                          xx cast(s32)(clip_max.x - clip_min.x), xx cast(s32)(clip_max.y - clip_min.y));

                // Bind texture, Draw
                glBindTexture(GL_TEXTURE_2D, cast(GLuint) cast(*void) pcmd.TextureId);
#if #exists(IMGUI_IMPL_OPENGL_MAY_HAVE_VTX_OFFSET) {
                if bd.GlVersion >= 320
                    glDrawElementsBaseVertex(GL_TRIANGLES, cast(GLsizei) pcmd.ElemCount,
                                             xx ifx size_of(ImGui.ImDrawIdx) == 2 then GL_UNSIGNED_SHORT else GL_UNSIGNED_INT,
                                                     cast(*void) cast(*void)(pcmd.IdxOffset * size_of(ImGui.ImDrawIdx)),
                                                     cast(GLint) pcmd.VtxOffset);
} else {
                glDrawElements(GL_TRIANGLES, cast(GLsizei) pcmd.ElemCount,
                               xx ifx size_of(ImGui.ImDrawIdx) == 2 then GL_UNSIGNED_SHORT else GL_UNSIGNED_INT,
                               cast(*void) cast(*void)(pcmd.IdxOffset * size_of(ImGui.ImDrawIdx)));
}
            }
        }
    }

    // Destroy the temporary VAO
#if #exists(IMGUI_IMPL_OPENGL_USE_VERTEX_ARRAY) {
    glDeleteVertexArrays(1, *vertex_array_object);
}

    // Restore modified GL state
    // This "glIsProgram()" check is required because if the program is "pending deletion" at the time of binding backup,
    // it will have been deleted by now and will cause an OpenGL error. See #6220.
    if last_program == 0 || glIsProgram(last_program) glUseProgram(last_program);
    glBindTexture(GL_TEXTURE_2D, last_texture);
#if #exists(IMGUI_IMPL_OPENGL_MAY_HAVE_BIND_SAMPLER) {
    if bd.GlVersion >= 330 || bd.GlProfileIsES3
        glBindSampler(0, last_sampler);
}
    glActiveTexture(last_active_texture);
#if #exists(IMGUI_IMPL_OPENGL_USE_VERTEX_ARRAY) {
    glBindVertexArray(last_vertex_array_object);
}
    glBindBuffer(GL_ARRAY_BUFFER, last_array_buffer);
#if !#exists(IMGUI_IMPL_OPENGL_USE_VERTEX_ARRAY) {
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, xx last_element_array_buffer);
    SetState(*last_vtx_attrib_state_pos, xx bd.AttribLocationVtxPos);
    SetState(*last_vtx_attrib_state_uv, xx bd.AttribLocationVtxUV);
    SetState(*last_vtx_attrib_state_color, xx bd.AttribLocationVtxColor);
}
    glBlendEquationSeparate(last_blend_equation_rgb, last_blend_equation_alpha);
    glBlendFuncSeparate(last_blend_src_rgb, last_blend_dst_rgb, last_blend_src_alpha, last_blend_dst_alpha);
    if last_enable_blend glEnable(GL_BLEND); else glDisable(GL_BLEND);
    if last_enable_cull_face glEnable(GL_CULL_FACE); else glDisable(GL_CULL_FACE);
    if last_enable_depth_test glEnable(GL_DEPTH_TEST); else glDisable(GL_DEPTH_TEST);
    if last_enable_stencil_test glEnable(GL_STENCIL_TEST); else glDisable(GL_STENCIL_TEST);
    if last_enable_scissor_test glEnable(GL_SCISSOR_TEST); else glDisable(GL_SCISSOR_TEST);
#if #exists(IMGUI_IMPL_OPENGL_MAY_HAVE_PRIMITIVE_RESTART) {
    if bd.GlVersion >= 310 {
        if last_enable_primitive_restart
            glEnable(GL_PRIMITIVE_RESTART);
        else
            glDisable(GL_PRIMITIVE_RESTART);
    }
}

#if #exists(IMGUI_IMPL_OPENGL_MAY_HAVE_POLYGON_MODE) {
    // Desktop OpenGL 3.0 and OpenGL 3.1 had separate polygon draw modes for front-facing and back-facing faces of polygons
    if (bd.HasPolygonMode) {
        if (bd.GlVersion <= 310 || bd.GlProfileIsCompat) {
            glPolygonMode(GL_FRONT, cast(GLenum) last_polygon_mode[0]);
            glPolygonMode(GL_BACK, cast(GLenum) last_polygon_mode[1]);
        } else {
            glPolygonMode(GL_FRONT_AND_BACK, cast(GLenum) last_polygon_mode[0]);
        }
    }
} // IMGUI_IMPL_OPENGL_MAY_HAVE_POLYGON_MODE

    glViewport(last_viewport[0], last_viewport[1], cast(GLsizei) last_viewport[2], cast(GLsizei) last_viewport[3]);
    glScissor(last_scissor_box[0], last_scissor_box[1], cast(GLsizei) last_scissor_box[2], cast(GLsizei) last_scissor_box[3]);
    //(void)bd; // Not all compilation paths use this
}

ImGui_ImplOpenGL3_CreateFontsTexture :: () -> bool {
    io : *ImGui.IO = ImGui.GetIO();
    bd : *ImGui_ImplOpenGL3_Data = ImGui_ImplOpenGL3_GetBackendData();

    // Build texture atlas
    pixels : *u8;
    width, height : s32;
    io.Fonts.GetTexDataAsRGBA32(io.Fonts, *pixels, *width, *height);   // Load as RGBA 32-bit (75% of the memory is wasted, but default font is so small) because it is more likely to be compatible with user's existing shaders. If your ImTextureId represent a higher-level concept than just a GL texture id, consider calling GetTexDataAsAlpha8() instead to save on GPU memory.

    // Upload texture to graphics system
    // (Bilinear sampling is required by default. Set 'io.Fonts.Flags |= ImFontAtlasFlags_NoBakedLines' or 'style.AntiAliasedLinesUseTex = false' to allow point/nearest sampling)
    last_texture : GLint;
    glGetIntegerv(GL_TEXTURE_BINDING_2D, *last_texture);
    glGenTextures(1, *bd.FontTexture);
    glBindTexture(GL_TEXTURE_2D, bd.FontTexture);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
#if GL_UNPACK_ROW_LENGTH { // Not on WebGL/ES
    glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
}
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, xx width, xx height, 0, GL_RGBA, GL_UNSIGNED_BYTE, pixels);

    // Store our identifier
    io.Fonts.TexID = cast(ImGui.ImTextureID) cast(*void) bd.FontTexture;

    // Restore state
    glBindTexture(GL_TEXTURE_2D, xx last_texture);

    return true;
}

ImGui_ImplOpenGL3_DestroyFontsTexture :: () {
    io : *ImGui.IO = ImGui.GetIO();
    bd : *ImGui_ImplOpenGL3_Data = ImGui_ImplOpenGL3_GetBackendData();
    if bd.FontTexture {
        glDeleteTextures(1, *bd.FontTexture);
        io.Fonts.TexID = xx 0;
        bd.FontTexture = 0;
    }
}

// If you get an error please report on github. You may try different GL context version or GLSL version.
// See GL<>GLSL version table at the top of this file.
CheckShader :: (handle: GLuint, desc: string) -> bool {
    bd : *ImGui_ImplOpenGL3_Data = ImGui_ImplOpenGL3_GetBackendData();
    status : GLint = 0;
    log_length : GLint = 0;
    glGetShaderiv(handle, GL_COMPILE_STATUS, *status);
    glGetShaderiv(handle, GL_INFO_LOG_LENGTH, *log_length);
    if cast(GLboolean) status == GL_FALSE
        print("ERROR: ImGui_ImplOpenGL3_CreateDeviceObjects: failed to compile %! With GLSL: %\n", desc,
              to_string(bd.GlslVersionString.data, c_style_strlen(bd.GlslVersionString.data)));
    if log_length > 1 && log_length < 1024 {
        buf : [1024]u8;
        glGetShaderInfoLog(handle, xx log_length, null, cast(*GLchar) buf.data);
        print("%\n", to_string(buf.data, c_style_strlen(buf.data)));
    }
    return cast(GLboolean)status == GL_TRUE;
}

// If you get an error please report on GitHub. You may try different GL context version or GLSL version.
CheckProgram :: (handle: GLuint, desc: string) -> bool {
    bd : *ImGui_ImplOpenGL3_Data = ImGui_ImplOpenGL3_GetBackendData();
    status : GLint = 0;
    log_length : GLint = 0;
    glGetProgramiv(handle, GL_LINK_STATUS, *status);
    glGetProgramiv(handle, GL_INFO_LOG_LENGTH, *log_length);
    if cast(GLboolean) status == GL_FALSE
        print("ERROR: ImGui_ImplOpenGL3_CreateDeviceObjects: failed to link %! With GLSL %\n", desc,
              to_string(bd.GlslVersionString.data, c_style_strlen(bd.GlslVersionString.data)));
    if log_length > 1 && log_length < 1024 {
        buf : [1024]u8;
        glGetProgramInfoLog(handle, xx log_length, null, cast(*GLchar) buf.data);
        print("%\n", to_string(buf.data, c_style_strlen(buf.data)));
    }
    return cast(GLboolean) status == GL_TRUE;
}

ImGui_ImplOpenGL3_CreateDeviceObjects :: () -> bool {
    bd : *ImGui_ImplOpenGL3_Data = ImGui_ImplOpenGL3_GetBackendData();

    // Backup GL state
    last_texture, last_array_buffer : GLint;
    glGetIntegerv(GL_TEXTURE_BINDING_2D, *last_texture);
    glGetIntegerv(GL_ARRAY_BUFFER_BINDING, *last_array_buffer);
#if #exists (IMGUI_IMPL_OPENGL_MAY_HAVE_BIND_BUFFER_PIXEL_UNPACK) {
    last_pixel_unpack_buffer : GLint = 0;
    if (bd.GlVersion >= 210) {
        glGetIntegerv(GL_PIXEL_UNPACK_BUFFER_BINDING, *last_pixel_unpack_buffer);
        glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0); }
}
#if #exists (IMGUI_IMPL_OPENGL_USE_VERTEX_ARRAY) {
    last_vertex_array : GLint;
    glGetIntegerv(GL_VERTEX_ARRAY_BINDING, *last_vertex_array);
}

    // Parse GLSL version string
    glsl_version : s32 = 130;
    matched, items := scan("#version %i", cast(string) bd.GlslVersionString);
    for items {
        if it.type.type == .INTEGER {
            glsl_version = << cast(*s32) items[0].value_pointer;
        }
    }

    vertex_shader_glsl_120 := #string DONE
        uniform mat4 ProjMtx;
        attribute vec2 Position;
        attribute vec2 UV;
        attribute vec4 Color;
        varying vec2 Frag_UV;
        varying vec4 Frag_Color;
        void main()
        {
            Frag_UV = UV;
            Frag_Color = Color;
            gl_Position = ProjMtx * vec4(Position.xy,0,1);
        }
DONE

    vertex_shader_glsl_130 := #string DONE
        uniform mat4 ProjMtx;
        in vec2 Position;
        in vec2 UV;
        in vec4 Color;
        out vec2 Frag_UV;
        out vec4 Frag_Color;
        void main()
        {
            Frag_UV = UV;
            Frag_Color = Color;
            gl_Position = ProjMtx * vec4(Position.xy,0,1);
        }
DONE

    vertex_shader_glsl_300_es := #string DONE
        precision highp float;
        layout (location = 0) in vec2 Position;
        layout (location = 1) in vec2 UV;
        layout (location = 2) in vec4 Color;
        uniform mat4 ProjMtx;
        out vec2 Frag_UV;
        out vec4 Frag_Color;
        void main()
        {
            Frag_UV = UV;
            Frag_Color = Color;
            gl_Position = ProjMtx * vec4(Position.xy,0,1);
        }
DONE

    vertex_shader_glsl_410_core := #string DONE
        layout (location = 0) in vec2 Position;
        layout (location = 1) in vec2 UV;
        layout (location = 2) in vec4 Color;
        uniform mat4 ProjMtx;
        out vec2 Frag_UV;
        out vec4 Frag_Color;
        void main()
        {
            Frag_UV = UV;
            Frag_Color = Color;
            gl_Position = ProjMtx * vec4(Position.xy,0,1);
        }
DONE

    fragment_shader_glsl_120 := #string DONE
        #ifdef GL_ES
            precision mediump float;
        #endif
        uniform sampler2D Texture;
        varying vec2 Frag_UV;
        varying vec4 Frag_Color;
        void main()
        {
            gl_FragColor = Frag_Color * texture2D(Texture, Frag_UV.st);
        }
DONE

    fragment_shader_glsl_130 := #string DONE
        uniform sampler2D Texture;
        in vec2 Frag_UV;
        in vec4 Frag_Color;
        out vec4 Out_Color;
        void main()
        {
            Out_Color = Frag_Color * texture(Texture, Frag_UV.st);
        }
DONE

    fragment_shader_glsl_300_es := #string DONE
        precision mediump float;
        uniform sampler2D Texture;
        in vec2 Frag_UV;
        in vec4 Frag_Color;
        layout (location = 0) out vec4 Out_Color;
        void main()
        {
            Out_Color = Frag_Color * texture(Texture, Frag_UV.st);
        }
DONE

    fragment_shader_glsl_410_core := #string DONE
        in vec2 Frag_UV;
        in vec4 Frag_Color;
        uniform sampler2D Texture;
        layout (location = 0) out vec4 Out_Color;
        void main()
        {
            Out_Color = Frag_Color * texture(Texture, Frag_UV.st);
        }
DONE

    // Select shaders matching our GLSL versions
    vertex_shader : string;
    fragment_shader : string;
    if (glsl_version < 130) {
        vertex_shader = vertex_shader_glsl_120;
        fragment_shader = fragment_shader_glsl_120;
    } else if (glsl_version >= 410) {
        vertex_shader = vertex_shader_glsl_410_core;
        fragment_shader = fragment_shader_glsl_410_core;
    } else if (glsl_version == 300) {
        vertex_shader = vertex_shader_glsl_300_es;
        fragment_shader = fragment_shader_glsl_300_es;
    } else {
        vertex_shader = vertex_shader_glsl_130;
        fragment_shader = fragment_shader_glsl_130;
    }

    // Create shaders
    vertex_shader_with_version : [2]*u8 = .[bd.GlslVersionString.data, vertex_shader.data];
    vertex_shader_with_version_length : [2]s32 = .[xx c_style_strlen(bd.GlslVersionString.data), xx vertex_shader.count];
    vert_handle : GLuint = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vert_handle, 2, vertex_shader_with_version.data, vertex_shader_with_version_length.data);
    glCompileShader(vert_handle);
    CheckShader(vert_handle, "vertex shader");

    fragment_shader_with_version : [2]*u8 = .[bd.GlslVersionString.data, fragment_shader.data];
    fragment_shader_with_version_length : [2]s32 = .[xx c_style_strlen(bd.GlslVersionString.data), xx fragment_shader.count];
    frag_handle : GLuint = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(frag_handle, 2, fragment_shader_with_version.data, fragment_shader_with_version_length.data);
    glCompileShader(frag_handle);
    CheckShader(frag_handle, "fragment shader");

    // Link
    bd.ShaderHandle = glCreateProgram();
    glAttachShader(bd.ShaderHandle, vert_handle);
    glAttachShader(bd.ShaderHandle, frag_handle);
    glLinkProgram(bd.ShaderHandle);
    CheckProgram(bd.ShaderHandle, "shader program");

    glDetachShader(bd.ShaderHandle, vert_handle);
    glDetachShader(bd.ShaderHandle, frag_handle);
    glDeleteShader(vert_handle);
    glDeleteShader(frag_handle);

    bd.AttribLocationTex = glGetUniformLocation(bd.ShaderHandle, "Texture");
    bd.AttribLocationProjMtx = glGetUniformLocation(bd.ShaderHandle, "ProjMtx");
    bd.AttribLocationVtxPos = cast(GLuint) glGetAttribLocation(bd.ShaderHandle, "Position");
    bd.AttribLocationVtxUV = cast(GLuint) glGetAttribLocation(bd.ShaderHandle, "UV");
    bd.AttribLocationVtxColor = cast(GLuint) glGetAttribLocation(bd.ShaderHandle, "Color");

    // Create buffers
    glGenBuffers(1, *bd.VboHandle);
    glGenBuffers(1, *bd.ElementsHandle);

    ImGui_ImplOpenGL3_CreateFontsTexture();

    // Restore modified GL state
    glBindTexture(GL_TEXTURE_2D, xx last_texture);
    glBindBuffer(GL_ARRAY_BUFFER, xx last_array_buffer);
#if #exists(IMGUI_IMPL_OPENGL_MAY_HAVE_BIND_BUFFER_PIXEL_UNPACK) {
    if (bd.GlVersion >= 210) {
        glBindBuffer(GL_PIXEL_UNPACK_BUFFER, xx last_pixel_unpack_buffer);
    }
}

#if #exists(IMGUI_IMPL_OPENGL_USE_VERTEX_ARRAY) {
    glBindVertexArray(xx last_vertex_array);
}

    return true;
}

ImGui_ImplOpenGL3_DestroyDeviceObjects :: () {
    bd : *ImGui_ImplOpenGL3_Data = ImGui_ImplOpenGL3_GetBackendData();
    if (bd.VboHandle)      { glDeleteBuffers(1, *bd.VboHandle); bd.VboHandle = 0; }
    if (bd.ElementsHandle) { glDeleteBuffers(1, *bd.ElementsHandle); bd.ElementsHandle = 0; }
    if (bd.ShaderHandle)   { glDeleteProgram(bd.ShaderHandle); bd.ShaderHandle = 0; }
    ImGui_ImplOpenGL3_DestroyFontsTexture();
}
