=====================================================
SDL源代码分析系列文章列表:
SDL2源代码分析1:初始化(SDL_Init())
SDL2源代码分析2:窗口(SDL_Window)
SDL2源代码分析3:渲染器(SDL_Renderer)
SDL2源代码分析4:纹理(SDL_Texture)
SDL2源代码分析5:更新纹理(SDL_UpdateTexture())
SDL2源代码分析6:复制到渲染器(SDL_RenderCopy())
SDL2源代码分析7:显示(SDL_RenderPresent())
SDL2源代码分析8:视频显示总结
=====================================================
上一篇文章分析了SDL中创建渲染器的函数SDL_CreateRenderer()。这篇文章继续分析SDL的源代码。本文分析SDL的纹理(SDL_Texture)。
SDL播放视频的代码流程如下所示。
初始化:
SDL_Init(): 初始化SDL。
SDL_CreateWindow(): 创建窗口(Window)。
SDL_CreateRenderer(): 基于窗口创建渲染器(Render)。
SDL_CreateTexture(): 创建纹理(Texture)。
循环渲染数据:
SDL_UpdateTexture(): 设置纹理的数据。
SDL_RenderCopy(): 纹理复制给渲染器。
SDL_RenderPresent(): 显示。
上篇文章分析了该流程中的第3个函数SDL_CreateRenderer()。本文继续分析该流程中的第4个函数SDL_CreateTexture()。
SDL_Texture
SDL_Texture结构定义了一个SDL中的纹理。如果直接使用SDL2编译好的SDK的话,是看不到SDL_Texture的内部结构的。有关它的定义在头文件中只有一行代码,如下所示。
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struct SDL_Texture;
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typedef struct SDL_Texture SDL_Texture;
在源代码工程中可以看到SDL_Texture的定义,位于render\SDL_sysrender.h文件中。它的定义如下。
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struct SDL_Texture
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{
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const void *magic;
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Uint32 format;
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int access;
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int w;
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int h;
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int modMode;
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SDL_BlendMode blendMode;
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Uint8 r, g, b, a;
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SDL_Renderer *renderer;
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SDL_Texture *native;
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SDL_SW_YUVTexture *yuv;
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void *pixels;
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int pitch;
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SDL_Rect locked_rect;
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void *driverdata;
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SDL_Texture *prev;
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SDL_Texture *next;
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};
可以看出其中包含了一个“纹理”所具备的各种属性。下面来看看如何创建这个SDL_Texture。
SDL_CreateTexture()
函数简介
使用SDL_CreateTexture()基于渲染器创建一个纹理。SDL_CreateTexture()的原型如下。
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SDL_Texture * SDLCALL SDL_CreateTexture(SDL_Renderer * renderer,
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Uint32 format,
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int access, int w,
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int h);
参数的含义如下。
renderer:目标渲染器。
format
:纹理的格式。后面会详述。
access :可以取以下值(定义位于SDL_TextureAccess中)
SDL_TEXTUREACCESS_STATIC
:变化极少
SDL_TEXTUREACCESS_STREAMING
:变化频繁
SDL_TEXTUREACCESS_TARGET :暂时没有理解
w :纹理的宽
h :纹理的高
创建成功则返回纹理的ID,失败返回0。
函数调用关系图
SDL_ CreateTexture ()关键函数的调用关系可以用下图表示。
上面的图片不太清晰,更清晰的图片上传到了相册里面:
http://my.csdn.net/leixiaohua1020/album/detail/1793543
把相册里面的图片保存下来就可以得到清晰的图片了。
源代码分析
SDL_CreateTexture()的源代码位于render\SDL_render.c中。如下所示。
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SDL_Texture * SDL_CreateTexture(SDL_Renderer * renderer, Uint32 format, int access, int w, int h)
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{
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SDL_Texture *texture;
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-
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CHECK_RENDERER_MAGIC(renderer, NULL);
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-
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if (!format) {
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format = renderer->info.texture_formats[0];
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}
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if (SDL_ISPIXELFORMAT_INDEXED(format)) {
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SDL_SetError("Palettized textures are not supported");
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return NULL;
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}
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if (w <= 0 || h <= 0) {
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SDL_SetError("Texture dimensions can't be 0");
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return NULL;
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}
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if ((renderer->info.max_texture_width && w > renderer->info.max_texture_width) ||
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(renderer->info.max_texture_height && h > renderer->info.max_texture_height)) {
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SDL_SetError("Texture dimensions are limited to %dx%d", renderer->info.max_texture_width, renderer->info.max_texture_height);
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return NULL;
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}
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texture = (SDL_Texture *) SDL_calloc(1, sizeof(*texture));
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if (!texture) {
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SDL_OutOfMemory();
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return NULL;
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}
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texture->magic = &texture_magic;
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texture->format = format;
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texture->access = access;
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texture->w = w;
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texture->h = h;
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texture->r = 255;
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texture->g = 255;
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texture->b = 255;
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texture->a = 255;
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texture->renderer = renderer;
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texture->next = renderer->textures;
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if (renderer->textures) {
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renderer->textures->prev = texture;
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}
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renderer->textures = texture;
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-
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if (IsSupportedFormat(renderer, format)) {
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if (renderer->CreateTexture(renderer, texture) < 0) {
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SDL_DestroyTexture(texture);
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return 0;
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}
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} else {
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texture->native = SDL_CreateTexture(renderer,
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GetClosestSupportedFormat(renderer, format),
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access, w, h);
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if (!texture->native) {
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SDL_DestroyTexture(texture);
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return NULL;
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}
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texture->native->next = texture->next;
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if (texture->native->next) {
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texture->native->next->prev = texture->native;
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}
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texture->prev = texture->native->prev;
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if (texture->prev) {
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texture->prev->next = texture;
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}
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texture->native->prev = texture;
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texture->next = texture->native;
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renderer->textures = texture;
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-
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if (SDL_ISPIXELFORMAT_FOURCC(texture->format)) {
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texture->yuv = SDL_SW_CreateYUVTexture(format, w, h);
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if (!texture->yuv) {
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SDL_DestroyTexture(texture);
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return NULL;
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}
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} else if (access == SDL_TEXTUREACCESS_STREAMING) {
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texture->pitch = (((w * SDL_BYTESPERPIXEL(format)) + 3) & ~3);
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texture->pixels = SDL_calloc(1, texture->pitch * h);
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if (!texture->pixels) {
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SDL_DestroyTexture(texture);
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return NULL;
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}
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}
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}
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return texture;
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}
从源代码中可以看出,SDL_CreateTexture()的大致流程如下。
1. 检查输入参数的合理性。例如像素格式是否支持,宽和高是否小于等于0等等。
2. 新建一个SDL_Texture。调用SDL_calloc()(实际上就是calloc())为新建的SDL_Texture分配内存。
3. 调用SDL_Render的CreateTexture()方法创建纹理。这一步是整个函数的核心。
下面我们详细看一下几种不同的渲染器的CreateTexture()的方法。
1.
Direct3D
Direct3D 渲染器中对应CreateTexture()的函数是D3D_CreateTexture(),它的源代码如下所示(位于render\direct3d\SDL_render_d3d.c)。
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static int D3D_CreateTexture(SDL_Renderer * renderer, SDL_Texture * texture)
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{
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D3D_RenderData *renderdata = (D3D_RenderData *) renderer->driverdata;
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D3D_TextureData *data;
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D3DPOOL pool;
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DWORD usage;
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HRESULT result;
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data = (D3D_TextureData *) SDL_calloc(1, sizeof(*data));
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if (!data) {
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return SDL_OutOfMemory();
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}
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data->scaleMode = GetScaleQuality();
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texture->driverdata = data;
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#ifdef USE_DYNAMIC_TEXTURE
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if (texture->access == SDL_TEXTUREACCESS_STREAMING) {
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pool = D3DPOOL_DEFAULT;
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usage = D3DUSAGE_DYNAMIC;
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} else
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#endif
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if (texture->access == SDL_TEXTUREACCESS_TARGET) {
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pool = D3DPOOL_DEFAULT;
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usage = D3DUSAGE_RENDERTARGET;
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} else {
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pool = D3DPOOL_MANAGED;
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usage = 0;
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}
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result =
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IDirect3DDevice9_CreateTexture(renderdata->device, texture->w,
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texture->h, 1, usage,
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PixelFormatToD3DFMT(texture->format),
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pool, &data->texture, NULL);
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if (FAILED(result)) {
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return D3D_SetError("CreateTexture()", result);
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}
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if (texture->format == SDL_PIXELFORMAT_YV12 ||
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texture->format == SDL_PIXELFORMAT_IYUV) {
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data->yuv = SDL_TRUE;
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result =
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IDirect3DDevice9_CreateTexture(renderdata->device, texture->w / 2,
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texture->h / 2, 1, usage,
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PixelFormatToD3DFMT(texture->format),
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pool, &data->utexture, NULL);
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if (FAILED(result)) {
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return D3D_SetError("CreateTexture()", result);
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}
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result =
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IDirect3DDevice9_CreateTexture(renderdata->device, texture->w / 2,
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texture->h / 2, 1, usage,
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PixelFormatToD3DFMT(texture->format),
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pool, &data->vtexture, NULL);
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if (FAILED(result)) {
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return D3D_SetError("CreateTexture()", result);
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}
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}
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return 0;
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}
从代码中可以看出,该函数调用了Direct3D的API函数IDirect3DDevice9_CreateTexture()创建了一个纹理。
2.
OpenGL
OpenGL渲染器中对应CreateTexture()的函数是GL_CreateTexture (),它的源代码如下所示(位于render\opengl\SDL_render_gl.c)。
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static int GL_CreateTexture(SDL_Renderer * renderer, SDL_Texture * texture)
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{
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GL_RenderData *renderdata = (GL_RenderData *) renderer->driverdata;
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GL_TextureData *data;
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GLint internalFormat;
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GLenum format, type;
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int texture_w, texture_h;
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GLenum scaleMode;
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GL_ActivateRenderer(renderer);
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if (!convert_format(renderdata, texture->format, &internalFormat,
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&format, &type)) {
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return SDL_SetError("Texture format %s not supported by OpenGL",
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SDL_GetPixelFormatName(texture->format));
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}
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data = (GL_TextureData *) SDL_calloc(1, sizeof(*data));
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if (!data) {
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return SDL_OutOfMemory();
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}
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if (texture->access == SDL_TEXTUREACCESS_STREAMING) {
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size_t size;
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data->pitch = texture->w * SDL_BYTESPERPIXEL(texture->format);
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size = texture->h * data->pitch;
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if (texture->format == SDL_PIXELFORMAT_YV12 ||
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texture->format == SDL_PIXELFORMAT_IYUV) {
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size += (2 * (texture->h * data->pitch) / 4);
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}
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data->pixels = SDL_calloc(1, size);
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if (!data->pixels) {
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SDL_free(data);
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return SDL_OutOfMemory();
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}
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}
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if (texture->access == SDL_TEXTUREACCESS_TARGET) {
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data->fbo = GL_GetFBO(renderdata, texture->w, texture->h);
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} else {
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data->fbo = NULL;
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}
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GL_CheckError("", renderer);
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renderdata->glGenTextures(1, &data->texture);
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if (GL_CheckError("glGenTexures()", renderer) < 0) {
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SDL_free(data);
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return -1;
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}
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texture->driverdata = data;
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if ((renderdata->GL_ARB_texture_rectangle_supported)
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){
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data->type = GL_TEXTURE_RECTANGLE_ARB;
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texture_w = texture->w;
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texture_h = texture->h;
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data->texw = (GLfloat) texture_w;
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data->texh = (GLfloat) texture_h;
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} else {
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data->type = GL_TEXTURE_2D;
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texture_w = power_of_2(texture->w);
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texture_h = power_of_2(texture->h);
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data->texw = (GLfloat) (texture->w) / texture_w;
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data->texh = (GLfloat) texture->h / texture_h;
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}
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data->format = format;
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data->formattype = type;
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scaleMode = GetScaleQuality();
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renderdata->glEnable(data->type);
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renderdata->glBindTexture(data->type, data->texture);
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renderdata->glTexParameteri(data->type, GL_TEXTURE_MIN_FILTER, scaleMode);
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renderdata->glTexParameteri(data->type, GL_TEXTURE_MAG_FILTER, scaleMode);
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if (data->type != GL_TEXTURE_RECTANGLE_ARB) {
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renderdata->glTexParameteri(data->type, GL_TEXTURE_WRAP_S,
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GL_CLAMP_TO_EDGE);
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renderdata->glTexParameteri(data->type, GL_TEXTURE_WRAP_T,
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GL_CLAMP_TO_EDGE);
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}
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#ifdef __MACOSX__
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#ifndef GL_TEXTURE_STORAGE_HINT_APPLE
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#define GL_TEXTURE_STORAGE_HINT_APPLE 0x85BC
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#endif
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#ifndef STORAGE_CACHED_APPLE
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#define STORAGE_CACHED_APPLE 0x85BE
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#endif
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#ifndef STORAGE_SHARED_APPLE
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#define STORAGE_SHARED_APPLE 0x85BF
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#endif
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if (texture->access == SDL_TEXTUREACCESS_STREAMING) {
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renderdata->glTexParameteri(data->type, GL_TEXTURE_STORAGE_HINT_APPLE,
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GL_STORAGE_SHARED_APPLE);
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} else {
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renderdata->glTexParameteri(data->type, GL_TEXTURE_STORAGE_HINT_APPLE,
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GL_STORAGE_CACHED_APPLE);
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}
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if (texture->access == SDL_TEXTUREACCESS_STREAMING
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&& texture->format == SDL_PIXELFORMAT_ARGB8888
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&& (texture->w % 8) == 0) {
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renderdata->glPixelStorei(GL_UNPACK_CLIENT_STORAGE_APPLE, GL_TRUE);
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renderdata->glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
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renderdata->glPixelStorei(GL_UNPACK_ROW_LENGTH,
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(data->pitch / SDL_BYTESPERPIXEL(texture->format)));
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renderdata->glTexImage2D(data->type, 0, internalFormat, texture_w,
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texture_h, 0, format, type, data->pixels);
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renderdata->glPixelStorei(GL_UNPACK_CLIENT_STORAGE_APPLE, GL_FALSE);
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}
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else
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#endif
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{
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renderdata->glTexImage2D(data->type, 0, internalFormat, texture_w,
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texture_h, 0, format, type, NULL);
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}
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renderdata->glDisable(data->type);
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if (GL_CheckError("glTexImage2D()", renderer) < 0) {
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return -1;
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}
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if (texture->format == SDL_PIXELFORMAT_YV12 ||
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texture->format == SDL_PIXELFORMAT_IYUV) {
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data->yuv = SDL_TRUE;
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renderdata->glGenTextures(1, &data->utexture);
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renderdata->glGenTextures(1, &data->vtexture);
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renderdata->glEnable(data->type);
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renderdata->glBindTexture(data->type, data->utexture);
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renderdata->glTexParameteri(data->type, GL_TEXTURE_MIN_FILTER,
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scaleMode);
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renderdata->glTexParameteri(data->type, GL_TEXTURE_MAG_FILTER,
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scaleMode);
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renderdata->glTexParameteri(data->type, GL_TEXTURE_WRAP_S,
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GL_CLAMP_TO_EDGE);
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renderdata->glTexParameteri(data->type, GL_TEXTURE_WRAP_T,
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GL_CLAMP_TO_EDGE);
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renderdata->glTexImage2D(data->type, 0, internalFormat, texture_w/2,
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texture_h/2, 0, format, type, NULL);
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renderdata->glBindTexture(data->type, data->vtexture);
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renderdata->glTexParameteri(data->type, GL_TEXTURE_MIN_FILTER,
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scaleMode);
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renderdata->glTexParameteri(data->type, GL_TEXTURE_MAG_FILTER,
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scaleMode);
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renderdata->glTexParameteri(data->type, GL_TEXTURE_WRAP_S,
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GL_CLAMP_TO_EDGE);
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renderdata->glTexParameteri(data->type, GL_TEXTURE_WRAP_T,
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GL_CLAMP_TO_EDGE);
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renderdata->glTexImage2D(data->type, 0, internalFormat, texture_w/2,
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texture_h/2, 0, format, type, NULL);
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-
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renderdata->glDisable(data->type);
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}
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-
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return GL_CheckError("", renderer);
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}
从代码中可以看出,该函数调用了OpenGL的API函数glGenTextures(),glBindTexture()创建了一个纹理。并且使用glTexParameteri()设置了有关的一些参数。
在这里有一点需要注意,在OpenGL渲染器中,如果输入像素格式是YV12或者IYUV,就会使用3个纹理。
3.
Software
Software渲染器中对应CreateTexture()的函数是SW_CreateTexture (),它的源代码如下所示(位于render\software\SDL_render_sw.c)。
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static int SW_CreateTexture(SDL_Renderer * renderer, SDL_Texture * texture)
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{
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int bpp;
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Uint32 Rmask, Gmask, Bmask, Amask;
-
-
-
if (!SDL_PixelFormatEnumToMasks
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(texture->format, &bpp, &Rmask, &Gmask, &Bmask, &Amask)) {
-
return SDL_SetError("Unknown texture format");
-
}
-
-
-
texture->driverdata =
-
SDL_CreateRGBSurface(0, texture->w, texture->h, bpp, Rmask, Gmask,
-
Bmask, Amask);
-
SDL_SetSurfaceColorMod(texture->driverdata, texture->r, texture->g,
-
texture->b);
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SDL_SetSurfaceAlphaMod(texture->driverdata, texture->a);
-
SDL_SetSurfaceBlendMode(texture->driverdata, texture->blendMode);
-
-
-
if (texture->access == SDL_TEXTUREACCESS_STATIC) {
-
SDL_SetSurfaceRLE(texture->driverdata, 1);
-
}
-
-
-
if (!texture->driverdata) {
-
return -1;
-
}
-
return 0;
-
}
该函数的源代码还没有详细分析。可以看出其中调用了SDL_CreateRGBSurface()创建了“Surface”。