/*
  Simple DirectMedia Layer
  Copyright (C) 1997-2011 Sam Lantinga <slouken@libsdl.org>

  This software is provided 'as-is', without any express or implied
  warranty.  In no event will the authors be held liable for any damages
  arising from the use of this software.

  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely, subject to the following restrictions:

  1. The origin of this software must not be misrepresented; you must not
     claim that you wrote the original software. If you use this software
     in a product, an acknowledgment in the product documentation would be
     appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be
     misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.
*/
#include "SDL_config.h"

#if SDL_VIDEO_RENDER_OGL && !SDL_RENDER_DISABLED

#include "SDL_hints.h"
#include "SDL_log.h"
#include "SDL_opengl.h"
#include "../SDL_sysrender.h"
#include "SDL_shaders_gl.h"

#ifdef __MACOSX__
#include <OpenGL/OpenGL.h>
#endif


/* OpenGL renderer implementation */

/* Details on optimizing the texture path on Mac OS X:
   http://developer.apple.com/library/mac/#documentation/GraphicsImaging/Conceptual/OpenGL-MacProgGuide/opengl_texturedata/opengl_texturedata.html
*/

/* Used to re-create the window with OpenGL capability */
extern int SDL_RecreateWindow(SDL_Window * window, Uint32 flags);

static const float inv255f = 1.0f / 255.0f;

static SDL_Renderer *GL_CreateRenderer(SDL_Window * window, Uint32 flags);
static void GL_WindowEvent(SDL_Renderer * renderer,
                           const SDL_WindowEvent *event);
static int GL_CreateTexture(SDL_Renderer * renderer, SDL_Texture * texture);
static int GL_UpdateTexture(SDL_Renderer * renderer, SDL_Texture * texture,
                            const SDL_Rect * rect, const void *pixels,
                            int pitch);
static int GL_LockTexture(SDL_Renderer * renderer, SDL_Texture * texture,
                          const SDL_Rect * rect, void **pixels, int *pitch);
static void GL_UnlockTexture(SDL_Renderer * renderer, SDL_Texture * texture);
static int GL_UpdateViewport(SDL_Renderer * renderer);
static int GL_RenderClear(SDL_Renderer * renderer);
static int GL_RenderDrawPoints(SDL_Renderer * renderer,
                               const SDL_Point * points, int count);
static int GL_RenderDrawLines(SDL_Renderer * renderer,
                              const SDL_Point * points, int count);
static int GL_RenderFillRects(SDL_Renderer * renderer,
                              const SDL_Rect * rects, int count);
static int GL_RenderCopy(SDL_Renderer * renderer, SDL_Texture * texture,
                         const SDL_Rect * srcrect, const SDL_Rect * dstrect);
static int GL_RenderReadPixels(SDL_Renderer * renderer, const SDL_Rect * rect,
                               Uint32 pixel_format, void * pixels, int pitch);
static void GL_RenderPresent(SDL_Renderer * renderer);
static void GL_DestroyTexture(SDL_Renderer * renderer, SDL_Texture * texture);
static void GL_DestroyRenderer(SDL_Renderer * renderer);


SDL_RenderDriver GL_RenderDriver = {
    GL_CreateRenderer,
    {
     "opengl",
     (SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC),
     1,
     {SDL_PIXELFORMAT_ARGB8888},
     0,
     0}
};

typedef struct
{
    SDL_GLContext context;
    SDL_bool GL_ARB_texture_rectangle_supported;
    struct {
        GL_Shader shader;
        Uint32 color;
        int blendMode;
    } current;

    /* OpenGL functions */
#define SDL_PROC(ret,func,params) ret (APIENTRY *func) params;
#include "SDL_glfuncs.h"
#undef SDL_PROC

    /* Multitexture support */
    SDL_bool GL_ARB_multitexture_supported;
    PFNGLACTIVETEXTUREARBPROC glActiveTextureARB;
    GLint num_texture_units;

    /* Shader support */
    GL_ShaderContext *shaders;

} GL_RenderData;

typedef struct
{
    GLuint texture;
    GLenum type;
    GLfloat texw;
    GLfloat texh;
    GLenum format;
    GLenum formattype;
    void *pixels;
    int pitch;
    SDL_Rect locked_rect;

    /* YV12 texture support */
    SDL_bool yuv;
    GLuint utexture;
    GLuint vtexture;
} GL_TextureData;


static void
GL_SetError(const char *prefix, GLenum result)
{
    const char *error;

    switch (result) {
    case GL_NO_ERROR:
        error = "GL_NO_ERROR";
        break;
    case GL_INVALID_ENUM:
        error = "GL_INVALID_ENUM";
        break;
    case GL_INVALID_VALUE:
        error = "GL_INVALID_VALUE";
        break;
    case GL_INVALID_OPERATION:
        error = "GL_INVALID_OPERATION";
        break;
    case GL_STACK_OVERFLOW:
        error = "GL_STACK_OVERFLOW";
        break;
    case GL_STACK_UNDERFLOW:
        error = "GL_STACK_UNDERFLOW";
        break;
    case GL_OUT_OF_MEMORY:
        error = "GL_OUT_OF_MEMORY";
        break;
    case GL_TABLE_TOO_LARGE:
        error = "GL_TABLE_TOO_LARGE";
        break;
    default:
        error = "UNKNOWN";
        break;
    }
    SDL_SetError("%s: %s", prefix, error);
}

static int
GL_LoadFunctions(GL_RenderData * data)
{
#ifdef __SDL_NOGETPROCADDR__
#define SDL_PROC(ret,func,params) data->func=func;
#else
#define SDL_PROC(ret,func,params) \
    do { \
        data->func = SDL_GL_GetProcAddress(#func); \
        if ( ! data->func ) { \
            SDL_SetError("Couldn't load GL function %s: %s\n", #func, SDL_GetError()); \
            return -1; \
        } \
    } while ( 0 );
#endif /* __SDL_NOGETPROCADDR__ */

#include "SDL_glfuncs.h"
#undef SDL_PROC
    return 0;
}

static SDL_GLContext SDL_CurrentContext = NULL;

static int
GL_ActivateRenderer(SDL_Renderer * renderer)
{
    GL_RenderData *data = (GL_RenderData *) renderer->driverdata;

    if (SDL_CurrentContext != data->context) {
        if (SDL_GL_MakeCurrent(renderer->window, data->context) < 0) {
            return -1;
        }
        SDL_CurrentContext = data->context;

        GL_UpdateViewport(renderer);
    }
    return 0;
}

/* This is called if we need to invalidate all of the SDL OpenGL state */
static void
GL_ResetState(SDL_Renderer *renderer)
{
    GL_RenderData *data = (GL_RenderData *) renderer->driverdata;

    if (SDL_CurrentContext == data->context) {
        GL_UpdateViewport(renderer);
    } else {
        GL_ActivateRenderer(renderer);
    }

    data->current.shader = SHADER_NONE;
    data->current.color = 0;
    data->current.blendMode = -1;

    data->glDisable(GL_DEPTH_TEST);
    data->glDisable(GL_CULL_FACE);
    /* This ended up causing video discrepancies between OpenGL and Direct3D */
    /*data->glEnable(GL_LINE_SMOOTH);*/

    data->glMatrixMode(GL_MODELVIEW);
    data->glLoadIdentity();
}

SDL_Renderer *
GL_CreateRenderer(SDL_Window * window, Uint32 flags)
{
    SDL_Renderer *renderer;
    GL_RenderData *data;
    const char *hint;
    GLint value;
    Uint32 window_flags;

    window_flags = SDL_GetWindowFlags(window);
    if (!(window_flags & SDL_WINDOW_OPENGL)) {
        if (SDL_RecreateWindow(window, window_flags | SDL_WINDOW_OPENGL) < 0) {
            return NULL;
        }
    }

    renderer = (SDL_Renderer *) SDL_calloc(1, sizeof(*renderer));
    if (!renderer) {
        SDL_OutOfMemory();
        return NULL;
    }

    data = (GL_RenderData *) SDL_calloc(1, sizeof(*data));
    if (!data) {
        GL_DestroyRenderer(renderer);
        SDL_OutOfMemory();
        return NULL;
    }

    renderer->WindowEvent = GL_WindowEvent;
    renderer->CreateTexture = GL_CreateTexture;
    renderer->UpdateTexture = GL_UpdateTexture;
    renderer->LockTexture = GL_LockTexture;
    renderer->UnlockTexture = GL_UnlockTexture;
    renderer->UpdateViewport = GL_UpdateViewport;
    renderer->RenderClear = GL_RenderClear;
    renderer->RenderDrawPoints = GL_RenderDrawPoints;
    renderer->RenderDrawLines = GL_RenderDrawLines;
    renderer->RenderFillRects = GL_RenderFillRects;
    renderer->RenderCopy = GL_RenderCopy;
    renderer->RenderReadPixels = GL_RenderReadPixels;
    renderer->RenderPresent = GL_RenderPresent;
    renderer->DestroyTexture = GL_DestroyTexture;
    renderer->DestroyRenderer = GL_DestroyRenderer;
    renderer->info = GL_RenderDriver.info;
    renderer->info.flags = SDL_RENDERER_ACCELERATED;
    renderer->driverdata = data;

    data->context = SDL_GL_CreateContext(window);
    if (!data->context) {
        GL_DestroyRenderer(renderer);
        return NULL;
    }
    if (SDL_GL_MakeCurrent(window, data->context) < 0) {
        GL_DestroyRenderer(renderer);
        return NULL;
    }

    if (GL_LoadFunctions(data) < 0) {
        GL_DestroyRenderer(renderer);
        return NULL;
    }

#ifdef __MACOSX__
    /* Enable multi-threaded rendering */
    /* Disabled until Ryan finishes his VBO/PBO code...
       CGLEnable(CGLGetCurrentContext(), kCGLCEMPEngine);
     */
#endif

    if (flags & SDL_RENDERER_PRESENTVSYNC) {
        SDL_GL_SetSwapInterval(1);
    } else {
        SDL_GL_SetSwapInterval(0);
    }
    if (SDL_GL_GetSwapInterval() > 0) {
        renderer->info.flags |= SDL_RENDERER_PRESENTVSYNC;
    }

    data->glGetIntegerv(GL_MAX_TEXTURE_SIZE, &value);
    renderer->info.max_texture_width = value;
    data->glGetIntegerv(GL_MAX_TEXTURE_SIZE, &value);
    renderer->info.max_texture_height = value;

    if (SDL_GL_ExtensionSupported("GL_ARB_texture_rectangle")
        || SDL_GL_ExtensionSupported("GL_EXT_texture_rectangle")) {
        data->GL_ARB_texture_rectangle_supported = SDL_TRUE;
    }

    /* Check for multitexture support */
    if (SDL_GL_ExtensionSupported("GL_ARB_multitexture")) {
        data->glActiveTextureARB = (PFNGLACTIVETEXTUREARBPROC) SDL_GL_GetProcAddress("glActiveTextureARB");
        if (data->glActiveTextureARB) {
            data->GL_ARB_multitexture_supported = SDL_TRUE;
            data->glGetIntegerv(GL_MAX_TEXTURE_UNITS_ARB, &data->num_texture_units);
        }
    }

    /* Check for shader support */
    hint = SDL_GetHint(SDL_HINT_RENDER_OPENGL_SHADERS);
    if (!hint || *hint != '0') {
        data->shaders = GL_CreateShaderContext();
    }
    SDL_LogInfo(SDL_LOG_CATEGORY_RENDER, "OpenGL shaders: %s",
                data->shaders ? "ENABLED" : "DISABLED");

    /* We support YV12 textures using 3 textures and a shader */
    if (data->shaders && data->num_texture_units >= 3) {
        renderer->info.texture_formats[renderer->info.num_texture_formats++] = SDL_PIXELFORMAT_YV12;
        renderer->info.texture_formats[renderer->info.num_texture_formats++] = SDL_PIXELFORMAT_IYUV;
    }

    /* Set up parameters for rendering */
    GL_ResetState(renderer);

    return renderer;
}

static void
GL_WindowEvent(SDL_Renderer * renderer, const SDL_WindowEvent *event)
{
    GL_RenderData *data = (GL_RenderData *) renderer->driverdata;

    if (event->event == SDL_WINDOWEVENT_SIZE_CHANGED) {
        /* Rebind the context to the window area and update matrices */
        SDL_CurrentContext = NULL;
    }
}

static __inline__ int
power_of_2(int input)
{
    int value = 1;

    while (value < input) {
        value <<= 1;
    }
    return value;
}

static __inline__ SDL_bool
convert_format(GL_RenderData *renderdata, Uint32 pixel_format,
               GLint* internalFormat, GLenum* format, GLenum* type)
{
    switch (pixel_format) {
    case SDL_PIXELFORMAT_ARGB8888:
        *internalFormat = GL_RGBA8;
        *format = GL_BGRA;
        *type = GL_UNSIGNED_INT_8_8_8_8_REV;
        break;
    case SDL_PIXELFORMAT_YV12:
    case SDL_PIXELFORMAT_IYUV:
        *internalFormat = GL_LUMINANCE;
        *format = GL_LUMINANCE;
        *type = GL_UNSIGNED_BYTE;
        break;
    default:
        return SDL_FALSE;
    }
    return SDL_TRUE;
}

static GLenum
GetScaleQuality(void)
{
    const char *hint = SDL_GetHint(SDL_HINT_RENDER_SCALE_QUALITY);

    if (!hint || *hint == '0' || SDL_strcasecmp(hint, "nearest") == 0) {
        return GL_NEAREST;
    } else {
        return GL_LINEAR;
    }
}

static int
GL_CreateTexture(SDL_Renderer * renderer, SDL_Texture * texture)
{
    GL_RenderData *renderdata = (GL_RenderData *) renderer->driverdata;
    GL_TextureData *data;
    GLint internalFormat;
    GLenum format, type;
    int texture_w, texture_h;
    GLenum scaleMode;
    GLenum result;

    GL_ActivateRenderer(renderer);

    if (!convert_format(renderdata, texture->format, &internalFormat,
                        &format, &type)) {
        SDL_SetError("Texture format %s not supported by OpenGL",
                     SDL_GetPixelFormatName(texture->format));
        return -1;
    }

    data = (GL_TextureData *) SDL_calloc(1, sizeof(*data));
    if (!data) {
        SDL_OutOfMemory();
        return -1;
    }

    if (texture->access == SDL_TEXTUREACCESS_STREAMING) {
        size_t size;
        data->pitch = texture->w * SDL_BYTESPERPIXEL(texture->format);
        size = texture->h * data->pitch;
        if (texture->format == SDL_PIXELFORMAT_YV12 ||
            texture->format == SDL_PIXELFORMAT_IYUV) {
            /* Need to add size for the U and V planes */
            size += (2 * (texture->h * data->pitch) / 4);
        }
        data->pixels = SDL_calloc(1, size);
        if (!data->pixels) {
            SDL_OutOfMemory();
            SDL_free(data);
            return -1;
        }
    }

    texture->driverdata = data;

    renderdata->glGetError();
    renderdata->glGenTextures(1, &data->texture);
    if (renderdata->GL_ARB_texture_rectangle_supported) {
        data->type = GL_TEXTURE_RECTANGLE_ARB;
        texture_w = texture->w;
        texture_h = texture->h;
        data->texw = (GLfloat) texture_w;
        data->texh = (GLfloat) texture_h;
    } else {
        data->type = GL_TEXTURE_2D;
        texture_w = power_of_2(texture->w);
        texture_h = power_of_2(texture->h);
        data->texw = (GLfloat) (texture->w) / texture_w;
        data->texh = (GLfloat) texture->h / texture_h;
    }

    data->format = format;
    data->formattype = type;
    scaleMode = GetScaleQuality();
    renderdata->glEnable(data->type);
    renderdata->glBindTexture(data->type, data->texture);
    renderdata->glTexParameteri(data->type, GL_TEXTURE_MIN_FILTER, scaleMode);
    renderdata->glTexParameteri(data->type, GL_TEXTURE_MAG_FILTER, scaleMode);
    renderdata->glTexParameteri(data->type, GL_TEXTURE_WRAP_S,
                                GL_CLAMP_TO_EDGE);
    renderdata->glTexParameteri(data->type, GL_TEXTURE_WRAP_T,
                                GL_CLAMP_TO_EDGE);
#ifdef __MACOSX__
#ifndef GL_TEXTURE_STORAGE_HINT_APPLE
#define GL_TEXTURE_STORAGE_HINT_APPLE       0x85BC
#endif
#ifndef STORAGE_CACHED_APPLE
#define STORAGE_CACHED_APPLE                0x85BE
#endif
#ifndef STORAGE_SHARED_APPLE
#define STORAGE_SHARED_APPLE                0x85BF
#endif
    if (texture->access == SDL_TEXTUREACCESS_STREAMING) {
        renderdata->glTexParameteri(data->type, GL_TEXTURE_STORAGE_HINT_APPLE,
                                    GL_STORAGE_SHARED_APPLE);
    } else {
        renderdata->glTexParameteri(data->type, GL_TEXTURE_STORAGE_HINT_APPLE,
                                    GL_STORAGE_CACHED_APPLE);
    }
    if (texture->access == SDL_TEXTUREACCESS_STREAMING
        && texture->format == SDL_PIXELFORMAT_ARGB8888
        && (texture->w % 8) == 0) {
        renderdata->glPixelStorei(GL_UNPACK_CLIENT_STORAGE_APPLE, GL_TRUE);
        renderdata->glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
        renderdata->glPixelStorei(GL_UNPACK_ROW_LENGTH,
                          (data->pitch / SDL_BYTESPERPIXEL(texture->format)));
        renderdata->glTexImage2D(data->type, 0, internalFormat, texture_w,
                                 texture_h, 0, format, type, data->pixels);
        renderdata->glPixelStorei(GL_UNPACK_CLIENT_STORAGE_APPLE, GL_FALSE);
    }
    else
#endif
    {
        renderdata->glTexImage2D(data->type, 0, internalFormat, texture_w,
                                 texture_h, 0, format, type, NULL);
    }
    renderdata->glDisable(data->type);
    result = renderdata->glGetError();
    if (result != GL_NO_ERROR) {
        GL_SetError("glTexImage2D()", result);
        return -1;
    }

    if (texture->format == SDL_PIXELFORMAT_YV12 ||
        texture->format == SDL_PIXELFORMAT_IYUV) {
        data->yuv = SDL_TRUE;

        renderdata->glGenTextures(1, &data->utexture);
        renderdata->glGenTextures(1, &data->vtexture);
        renderdata->glEnable(data->type);

        renderdata->glBindTexture(data->type, data->utexture);
        renderdata->glTexParameteri(data->type, GL_TEXTURE_MIN_FILTER,
                                    scaleMode);
        renderdata->glTexParameteri(data->type, GL_TEXTURE_MAG_FILTER,
                                    scaleMode);
        renderdata->glTexParameteri(data->type, GL_TEXTURE_WRAP_S,
                                    GL_CLAMP_TO_EDGE);
        renderdata->glTexParameteri(data->type, GL_TEXTURE_WRAP_T,
                                    GL_CLAMP_TO_EDGE);
        renderdata->glTexImage2D(data->type, 0, internalFormat, texture_w/2,
                                 texture_h/2, 0, format, type, NULL);

        renderdata->glBindTexture(data->type, data->vtexture);
        renderdata->glTexParameteri(data->type, GL_TEXTURE_MIN_FILTER,
                                    scaleMode);
        renderdata->glTexParameteri(data->type, GL_TEXTURE_MAG_FILTER,
                                    scaleMode);
        renderdata->glTexParameteri(data->type, GL_TEXTURE_WRAP_S,
                                    GL_CLAMP_TO_EDGE);
        renderdata->glTexParameteri(data->type, GL_TEXTURE_WRAP_T,
                                    GL_CLAMP_TO_EDGE);
        renderdata->glTexImage2D(data->type, 0, internalFormat, texture_w/2,
                                 texture_h/2, 0, format, type, NULL);

        renderdata->glDisable(data->type);
    }
    return 0;
}

static int
GL_UpdateTexture(SDL_Renderer * renderer, SDL_Texture * texture,
                 const SDL_Rect * rect, const void *pixels, int pitch)
{
    GL_RenderData *renderdata = (GL_RenderData *) renderer->driverdata;
    GL_TextureData *data = (GL_TextureData *) texture->driverdata;
    GLenum result;

    GL_ActivateRenderer(renderer);

    renderdata->glGetError();
    renderdata->glEnable(data->type);
    renderdata->glBindTexture(data->type, data->texture);
    renderdata->glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
    renderdata->glPixelStorei(GL_UNPACK_ROW_LENGTH,
                              (pitch / SDL_BYTESPERPIXEL(texture->format)));
    renderdata->glTexSubImage2D(data->type, 0, rect->x, rect->y, rect->w,
                                rect->h, data->format, data->formattype,
                                pixels);
    if (data->yuv) {
        const void *top;

        renderdata->glPixelStorei(GL_UNPACK_ROW_LENGTH, (pitch / 2));

        /* Skip to the top of the next texture */
        top = (const void*)((const Uint8*)pixels + (texture->h-rect->y) * pitch - rect->x);

        /* Skip to the correct offset into the next texture */
        pixels = (const void*)((const Uint8*)top + (rect->y / 2) * pitch + rect->x / 2);
        if (texture->format == SDL_PIXELFORMAT_YV12) {
            renderdata->glBindTexture(data->type, data->vtexture);
        } else {
            renderdata->glBindTexture(data->type, data->utexture);
        }
        renderdata->glTexSubImage2D(data->type, 0, rect->x/2, rect->y/2,
                                    rect->w/2, rect->h/2,
                                    data->format, data->formattype, pixels);

        /* Skip to the top of the next texture */
        top = (const void*)((const Uint8*)top + (texture->h * pitch)/4);

        /* Skip to the correct offset into the next texture */
        pixels = (const void*)((const Uint8*)top + (rect->y / 2) * pitch + rect->x / 2);
        if (texture->format == SDL_PIXELFORMAT_YV12) {
            renderdata->glBindTexture(data->type, data->utexture);
        } else {
            renderdata->glBindTexture(data->type, data->vtexture);
        }
        renderdata->glTexSubImage2D(data->type, 0, rect->x/2, rect->y/2,
                                    rect->w/2, rect->h/2,
                                    data->format, data->formattype, pixels);
    }
    renderdata->glDisable(data->type);
    result = renderdata->glGetError();
    if (result != GL_NO_ERROR) {
        GL_SetError("glTexSubImage2D()", result);
        return -1;
    }
    return 0;
}

static int
GL_LockTexture(SDL_Renderer * renderer, SDL_Texture * texture,
               const SDL_Rect * rect, void **pixels, int *pitch)
{
    GL_TextureData *data = (GL_TextureData *) texture->driverdata;

    data->locked_rect = *rect;
    *pixels = 
        (void *) ((Uint8 *) data->pixels + rect->y * data->pitch +
                  rect->x * SDL_BYTESPERPIXEL(texture->format));
    *pitch = data->pitch;
    return 0;
}

static void
GL_UnlockTexture(SDL_Renderer * renderer, SDL_Texture * texture)
{
    GL_TextureData *data = (GL_TextureData *) texture->driverdata;
    const SDL_Rect *rect;
    void *pixels;

    rect = &data->locked_rect;
    pixels = 
        (void *) ((Uint8 *) data->pixels + rect->y * data->pitch +
                  rect->x * SDL_BYTESPERPIXEL(texture->format));
    GL_UpdateTexture(renderer, texture, rect, pixels, data->pitch);
}

static int
GL_UpdateViewport(SDL_Renderer * renderer)
{
    GL_RenderData *data = (GL_RenderData *) renderer->driverdata;

    if (SDL_CurrentContext != data->context) {
        /* We'll update the viewport after we rebind the context */
        return 0;
    }

    data->glViewport(renderer->viewport.x, renderer->viewport.y,
                     renderer->viewport.w, renderer->viewport.h);

    data->glMatrixMode(GL_PROJECTION);
    data->glLoadIdentity();
    data->glOrtho((GLdouble) 0,
                  (GLdouble) renderer->viewport.w,
                  (GLdouble) renderer->viewport.h,
                  (GLdouble) 0, 0.0, 1.0);
    return 0;
}

static void
GL_SetShader(GL_RenderData * data, GL_Shader shader)
{
    if (data->shaders && shader != data->current.shader) {
        GL_SelectShader(data->shaders, shader);
        data->current.shader = shader;
    }
}

static void
GL_SetColor(GL_RenderData * data, Uint8 r, Uint8 g, Uint8 b, Uint8 a)
{
    Uint32 color = ((a << 24) | (r << 16) | (g << 8) | b);

    if (color != data->current.color) {
        data->glColor4f((GLfloat) r * inv255f,
                        (GLfloat) g * inv255f,
                        (GLfloat) b * inv255f,
                        (GLfloat) a * inv255f);
        data->current.color = color;
    }
}

static void
GL_SetBlendMode(GL_RenderData * data, int blendMode)
{
    if (blendMode != data->current.blendMode) {
        switch (blendMode) {
        case SDL_BLENDMODE_NONE:
            data->glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
            data->glDisable(GL_BLEND);
            break;
        case SDL_BLENDMODE_BLEND:
            data->glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
            data->glEnable(GL_BLEND);
            data->glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
            break;
        case SDL_BLENDMODE_ADD:
            data->glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
            data->glEnable(GL_BLEND);
            data->glBlendFunc(GL_SRC_ALPHA, GL_ONE);
            break;
        case SDL_BLENDMODE_MOD:
            data->glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
            data->glEnable(GL_BLEND);
            data->glBlendFunc(GL_ZERO, GL_SRC_COLOR);
            break;
        }
        data->current.blendMode = blendMode;
    }
}

static void
GL_SetDrawingState(SDL_Renderer * renderer)
{
    GL_RenderData *data = (GL_RenderData *) renderer->driverdata;

    GL_ActivateRenderer(renderer);

    GL_SetColor(data, renderer->r,
                      renderer->g,
                      renderer->b,
                      renderer->a);

    GL_SetBlendMode(data, renderer->blendMode);

    GL_SetShader(data, SHADER_SOLID);
}

static int
GL_RenderClear(SDL_Renderer * renderer)
{
    GL_RenderData *data = (GL_RenderData *) renderer->driverdata;

    GL_ActivateRenderer(renderer);

    data->glClearColor((GLfloat) renderer->r * inv255f,
                       (GLfloat) renderer->g * inv255f,
                       (GLfloat) renderer->b * inv255f,
                       (GLfloat) renderer->a * inv255f);

    data->glClear(GL_COLOR_BUFFER_BIT);

    return 0;
}

static int
GL_RenderDrawPoints(SDL_Renderer * renderer, const SDL_Point * points,
                    int count)
{
    GL_RenderData *data = (GL_RenderData *) renderer->driverdata;
    int i;

    GL_SetDrawingState(renderer);

    data->glBegin(GL_POINTS);
    for (i = 0; i < count; ++i) {
        data->glVertex2f(0.5f + points[i].x, 0.5f + points[i].y);
    }
    data->glEnd();

    return 0;
}

static int
GL_RenderDrawLines(SDL_Renderer * renderer, const SDL_Point * points,
                   int count)
{
    GL_RenderData *data = (GL_RenderData *) renderer->driverdata;
    int i;

    GL_SetDrawingState(renderer);

    if (count > 2 && 
        points[0].x == points[count-1].x && points[0].y == points[count-1].y) {
        data->glBegin(GL_LINE_LOOP);
        /* GL_LINE_LOOP takes care of the final segment */
        --count;
        for (i = 0; i < count; ++i) {
            data->glVertex2f(0.5f + points[i].x, 0.5f + points[i].y);
        }
        data->glEnd();
    } else {
#if defined(__APPLE__) || defined(__WIN32__)
#else
        int x1, y1, x2, y2;
#endif

        data->glBegin(GL_LINE_STRIP);
        for (i = 0; i < count; ++i) {
            data->glVertex2f(0.5f + points[i].x, 0.5f + points[i].y);
        }
        data->glEnd();

        /* The line is half open, so we need one more point to complete it.
         * http://www.opengl.org/documentation/specs/version1.1/glspec1.1/node47.html
         * If we have to, we can use vertical line and horizontal line textures
         * for vertical and horizontal lines, and then create custom textures
         * for diagonal lines and software render those.  It's terrible, but at
         * least it would be pixel perfect.
         */
        data->glBegin(GL_POINTS);
#if defined(__APPLE__) || defined(__WIN32__)
        /* Mac OS X and Windows seem to always leave the second point open */
        data->glVertex2f(0.5f + points[count-1].x, 0.5f + points[count-1].y);
#else
        /* Linux seems to leave the right-most or bottom-most point open */
        x1 = points[0].x;
        y1 = points[0].y;
        x2 = points[count-1].x;
        y2 = points[count-1].y;

        if (x1 > x2) {
            data->glVertex2f(0.5f + x1, 0.5f + y1);
        } else if (x2 > x1) {
            data->glVertex2f(0.5f + x2, 0.5f + y2);
        } else if (y1 > y2) {
            data->glVertex2f(0.5f + x1, 0.5f + y1);
        } else if (y2 > y1) {
            data->glVertex2f(0.5f + x2, 0.5f + y2);
        }
#endif
        data->glEnd();
    }

    return 0;
}

static int
GL_RenderFillRects(SDL_Renderer * renderer, const SDL_Rect * rects, int count)
{
    GL_RenderData *data = (GL_RenderData *) renderer->driverdata;
    int i;

    GL_SetDrawingState(renderer);

    for (i = 0; i < count; ++i) {
        const SDL_Rect *rect = &rects[i];

        data->glRecti(rect->x, rect->y, rect->x + rect->w, rect->y + rect->h);
    }

    return 0;
}

static int
GL_RenderCopy(SDL_Renderer * renderer, SDL_Texture * texture,
              const SDL_Rect * srcrect, const SDL_Rect * dstrect)
{
    GL_RenderData *data = (GL_RenderData *) renderer->driverdata;
    GL_TextureData *texturedata = (GL_TextureData *) texture->driverdata;
    int minx, miny, maxx, maxy;
    GLfloat minu, maxu, minv, maxv;

    GL_ActivateRenderer(renderer);

    data->glEnable(texturedata->type);
    if (texturedata->yuv) {
        data->glActiveTextureARB(GL_TEXTURE2_ARB);
        data->glBindTexture(texturedata->type, texturedata->vtexture);

        data->glActiveTextureARB(GL_TEXTURE1_ARB);
        data->glBindTexture(texturedata->type, texturedata->utexture);

        data->glActiveTextureARB(GL_TEXTURE0_ARB);
    }
    data->glBindTexture(texturedata->type, texturedata->texture);

    if (texture->modMode) {
        GL_SetColor(data, texture->r, texture->g, texture->b, texture->a);
    } else {
        GL_SetColor(data, 255, 255, 255, 255);
    }

    GL_SetBlendMode(data, texture->blendMode);

    if (texturedata->yuv) {
        GL_SetShader(data, SHADER_YV12);
    } else {
        GL_SetShader(data, SHADER_RGB);
    }

    minx = dstrect->x;
    miny = dstrect->y;
    maxx = dstrect->x + dstrect->w;
    maxy = dstrect->y + dstrect->h;

    minu = (GLfloat) srcrect->x / texture->w;
    minu *= texturedata->texw;
    maxu = (GLfloat) (srcrect->x + srcrect->w) / texture->w;
    maxu *= texturedata->texw;
    minv = (GLfloat) srcrect->y / texture->h;
    minv *= texturedata->texh;
    maxv = (GLfloat) (srcrect->y + srcrect->h) / texture->h;
    maxv *= texturedata->texh;

    data->glBegin(GL_TRIANGLE_STRIP);
    data->glTexCoord2f(minu, minv);
    data->glVertex2f((GLfloat) minx, (GLfloat) miny);
    data->glTexCoord2f(maxu, minv);
    data->glVertex2f((GLfloat) maxx, (GLfloat) miny);
    data->glTexCoord2f(minu, maxv);
    data->glVertex2f((GLfloat) minx, (GLfloat) maxy);
    data->glTexCoord2f(maxu, maxv);
    data->glVertex2f((GLfloat) maxx, (GLfloat) maxy);
    data->glEnd();

    data->glDisable(texturedata->type);

    return 0;
}

static int
GL_RenderReadPixels(SDL_Renderer * renderer, const SDL_Rect * rect,
                    Uint32 pixel_format, void * pixels, int pitch)
{
    GL_RenderData *data = (GL_RenderData *) renderer->driverdata;
    SDL_Window *window = renderer->window;
    Uint32 temp_format = SDL_PIXELFORMAT_ARGB8888;
    void *temp_pixels;
    int temp_pitch;
    GLint internalFormat;
    GLenum format, type;
    Uint8 *src, *dst, *tmp;
    int w, h, length, rows;
    int status;

    GL_ActivateRenderer(renderer);

    temp_pitch = rect->w * SDL_BYTESPERPIXEL(temp_format);
    temp_pixels = SDL_malloc(rect->h * temp_pitch);
    if (!temp_pixels) {
        SDL_OutOfMemory();
        return -1;
    }

    convert_format(data, temp_format, &internalFormat, &format, &type);

    SDL_GetWindowSize(window, &w, &h);

    data->glPixelStorei(GL_PACK_ALIGNMENT, 1);
    data->glPixelStorei(GL_PACK_ROW_LENGTH,
                        (temp_pitch / SDL_BYTESPERPIXEL(temp_format)));

    data->glReadPixels(rect->x, (h-rect->y)-rect->h, rect->w, rect->h,
                       format, type, temp_pixels);

    /* Flip the rows to be top-down */
    length = rect->w * SDL_BYTESPERPIXEL(temp_format);
    src = (Uint8*)temp_pixels + (rect->h-1)*temp_pitch;
    dst = (Uint8*)temp_pixels;
    tmp = SDL_stack_alloc(Uint8, length);
    rows = rect->h / 2;
    while (rows--) {
        SDL_memcpy(tmp, dst, length);
        SDL_memcpy(dst, src, length);
        SDL_memcpy(src, tmp, length);
        dst += temp_pitch;
        src -= temp_pitch;
    }
    SDL_stack_free(tmp);

    status = SDL_ConvertPixels(rect->w, rect->h,
                               temp_format, temp_pixels, temp_pitch,
                               pixel_format, pixels, pitch);
    SDL_free(temp_pixels);

    return status;
}

static void
GL_RenderPresent(SDL_Renderer * renderer)
{
    GL_ActivateRenderer(renderer);

    SDL_GL_SwapWindow(renderer->window);
}

static void
GL_DestroyTexture(SDL_Renderer * renderer, SDL_Texture * texture)
{
    GL_RenderData *renderdata = (GL_RenderData *) renderer->driverdata;
    GL_TextureData *data = (GL_TextureData *) texture->driverdata;

    GL_ActivateRenderer(renderer);

    if (!data) {
        return;
    }
    if (data->texture) {
        renderdata->glDeleteTextures(1, &data->texture);
    }
    if (data->yuv) {
        renderdata->glDeleteTextures(1, &data->utexture);
        renderdata->glDeleteTextures(1, &data->vtexture);
    }
    if (data->pixels) {
        SDL_free(data->pixels);
    }
    SDL_free(data);
    texture->driverdata = NULL;
}

static void
GL_DestroyRenderer(SDL_Renderer * renderer)
{
    GL_RenderData *data = (GL_RenderData *) renderer->driverdata;

    if (data) {
        if (data->context) {
            /* SDL_GL_MakeCurrent(0, NULL); *//* doesn't do anything */
            SDL_GL_DeleteContext(data->context);
        }
        SDL_free(data);
    }
    SDL_free(renderer);
}

#endif /* SDL_VIDEO_RENDER_OGL && !SDL_RENDER_DISABLED */

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