=====================================================
SDL源代码分析系列文章列表：
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()）
=====================================================
上一篇文章分析了SDL更新纹理像素数据的函数SDL_UpdateTexture()。这篇文章继续分析SDL的源代码。本文分析SDL纹理复制到渲染目标的函数SDL_RenderCopy()。
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5个函数SDL_UpdateTexture()。本文继续分析该流程中的第6个函数SDL_RenderCopy()。
SDL_RenderCopy()
函数简介
SDL使用SDL_RenderCopy()将纹理数据复制给渲染目标。SDL_RenderCopy()的原型如下。
int SDLCALL SDL_RenderCopy(SDL_Renderer * renderer,
SDL_Texture * texture,
const SDL_Rect * srcrect,
const SDL_Rect * dstrect);
参数的含义如下。
renderer：渲染目标。
texture：输入纹理。
srcrect：选择输入纹理的一块矩形区域作为输入。设置为NULL的时候整个纹理作为输入。
dstrect：选择渲染目标的一块矩形区域作为输出。设置为NULL的时候整个渲染目标作为输出。
成功的话返回0，失败的话返回-1。
函数调用关系图
SDL_RenderCopy()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/1793911
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_RenderCopy()的源代码位于render\SDL_render.c中，如下所示。
int SDL_RenderCopy(SDL_Renderer * renderer, SDL_Texture * texture,
const SDL_Rect * srcrect, const SDL_Rect * dstrect)
{
SDL_Rect real_srcrect = { 0, 0, 0, 0 };
SDL_Rect real_dstrect = { 0, 0, 0, 0 };
SDL_FRect frect;
CHECK_RENDERER_MAGIC(renderer, -1);
CHECK_TEXTURE_MAGIC(texture, -1);
if (renderer != texture->renderer) {
return SDL_SetError("Texture was not created with this renderer");
}
real_srcrect.x = 0;
real_srcrect.y = 0;
real_srcrect.w = texture->w;
real_srcrect.h = texture->h;
if (srcrect) {
if (!SDL_IntersectRect(srcrect, &real_srcrect, &real_srcrect)) {
return 0;
}
}
SDL_RenderGetViewport(renderer, &real_dstrect);
real_dstrect.x = 0;
real_dstrect.y = 0;
if (dstrect) {
if (!SDL_HasIntersection(dstrect, &real_dstrect)) {
return 0;
}
real_dstrect = *dstrect;
}
if (texture->native) {
texture = texture->native;
}
/* Don't draw while we're hidden */
if (renderer->hidden) {
return 0;
}
frect.x = real_dstrect.x * renderer->scale.x;
frect.y = real_dstrect.y * renderer->scale.y;
frect.w = real_dstrect.w * renderer->scale.x;
frect.h = real_dstrect.h * renderer->scale.y;
return renderer->RenderCopy(renderer, texture, &real_srcrect, &frect);
}
从源代码中可以看出，SDL_RenderCopy()的大致流程如下。
1. 检查输入参数的合理性。
2. 调用SDL_Render的RenderCopy ()方法复制纹理到渲染目标。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RenderCopy()的方法。
1. Direct3D
Direct3D 渲染器中对应RenderCopy()的函数是D3D_RenderCopy()，它的源代码如下所示（位于render\direct3d\SDL_render_d3d.c）。
static int D3D_RenderCopy(SDL_Renderer * renderer, SDL_Texture * texture,
const SDL_Rect * srcrect, const SDL_FRect * dstrect)
{
D3D_RenderData *data = (D3D_RenderData *) renderer->driverdata;
D3D_TextureData *texturedata;
LPDIRECT3DPIXELSHADER9 shader = NULL;
float minx, miny, maxx, maxy;
float minu, maxu, minv, maxv;
DWORD color;
Vertex vertices[4];
HRESULT result;
if (D3D_ActivateRenderer(renderer) < 0) {
return -1;
}
texturedata = (D3D_TextureData *)texture->driverdata;
if (!texturedata) {
SDL_SetError("Texture is not currently available");
return -1;
}
minx = dstrect->x - 0.5f;
miny = dstrect->y - 0.5f;
maxx = dstrect->x + dstrect->w - 0.5f;
maxy = dstrect->y + dstrect->h - 0.5f;
minu = (float) srcrect->x / texture->w;
maxu = (float) (srcrect->x + srcrect->w) / texture->w;
minv = (float) srcrect->y / texture->h;
maxv = (float) (srcrect->y + srcrect->h) / texture->h;
color = D3DCOLOR_ARGB(texture->a, texture->r, texture->g, texture->b);
vertices[0].x = minx;
vertices[0].y = miny;
vertices[0].z = 0.0f;
vertices[0].color = color;
vertices[0].u = minu;
vertices[0].v = minv;
vertices[1].x = maxx;
vertices[1].y = miny;
vertices[1].z = 0.0f;
vertices[1].color = color;
vertices[1].u = maxu;
vertices[1].v = minv;
vertices[2].x = maxx;
vertices[2].y = maxy;
vertices[2].z = 0.0f;
vertices[2].color = color;
vertices[2].u = maxu;
vertices[2].v = maxv;
vertices[3].x = minx;
vertices[3].y = maxy;
vertices[3].z = 0.0f;
vertices[3].color = color;
vertices[3].u = minu;
vertices[3].v = maxv;
D3D_SetBlendMode(data, texture->blendMode);
D3D_UpdateTextureScaleMode(data, texturedata, 0);
result =
IDirect3DDevice9_SetTexture(data->device, 0, (IDirect3DBaseTexture9 *)
texturedata->texture);
if (FAILED(result)) {
return D3D_SetError("SetTexture()", result);
}
if (texturedata->yuv) {
shader = data->ps_yuv;
D3D_UpdateTextureScaleMode(data, texturedata, 1);
D3D_UpdateTextureScaleMode(data, texturedata, 2);
result =
IDirect3DDevice9_SetTexture(data->device, 1, (IDirect3DBaseTexture9 *)
texturedata->utexture);
if (FAILED(result)) {
return D3D_SetError("SetTexture()", result);
}
result =
IDirect3DDevice9_SetTexture(data->device, 2, (IDirect3DBaseTexture9 *)
texturedata->vtexture);
if (FAILED(result)) {
return D3D_SetError("SetTexture()", result);
}
}
if (shader) {
result = IDirect3DDevice9_SetPixelShader(data->device, shader);
if (FAILED(result)) {
return D3D_SetError("SetShader()", result);
}
}
result =
IDirect3DDevice9_DrawPrimitiveUP(data->device, D3DPT_TRIANGLEFAN, 2,
vertices, sizeof(*vertices));
if (FAILED(result)) {
return D3D_SetError("DrawPrimitiveUP()", result);
}
if (shader) {
result = IDirect3DDevice9_SetPixelShader(data->device, NULL);
if (FAILED(result)) {
return D3D_SetError("SetShader()", result);
}
}
return 0;
}
从代码中可以看出，D3D_RenderCopy()函数按照执行的顺序调用了如下函数：
D3D_ActivateRenderer()：激活渲染器。其内部使用Direct3D的API函数IDirect3DDevice9_BeginScene()开始一个D3D的场景。
D3D_SetBlendMode()：设置渲染器状态。其内部使用Direct3D的API函数IDirect3DDevice9_SetRenderState()设置渲染器的状态。
D3D_UpdateTextureScaleMode()：设置纹理采样方式。其内部调用使用Direct3D的API函数IDirect3DDevice9_SetSamplerState()设置D3D的纹理采样方式。
IDirect3DDevice9_SetTexture()：Direct3D的API，用于设置当前启用的纹理。
IDirect3DDevice9_SetPixelShader()：Direct3D的API，用于设置使用的像素着色器。IDirect3DDevice9_DrawPrimitiveUP()：Direct3D的API，用于渲染。
上述几个函数中，前3个函数是SDL中的函数，后3个函数是Direct3D的API。在此附上前三个函数的代码。
D3D_ActivateRenderer()：激活渲染器。
static int D3D_ActivateRenderer(SDL_Renderer * renderer)
{
D3D_RenderData *data = (D3D_RenderData *) renderer->driverdata;
HRESULT result;
if (data->updateSize) {
SDL_Window *window = renderer->window;
int w, h;
SDL_GetWindowSize(window, &w, &h);
data->pparams.BackBufferWidth = w;
data->pparams.BackBufferHeight = h;
if (SDL_GetWindowFlags(window) & SDL_WINDOW_FULLSCREEN) {
data->pparams.BackBufferFormat =
PixelFormatToD3DFMT(SDL_GetWindowPixelFormat(window));
} else {
data->pparams.BackBufferFormat = D3DFMT_UNKNOWN;
}
if (D3D_Reset(renderer) < 0) {
return -1;
}
data->updateSize = SDL_FALSE;
}
if (data->beginScene) {
result = IDirect3DDevice9_BeginScene(data->device);
if (result == D3DERR_DEVICELOST) {
if (D3D_Reset(renderer) < 0) {
return -1;
}
result = IDirect3DDevice9_BeginScene(data->device);
}
if (FAILED(result)) {
return D3D_SetError("BeginScene()", result);
}
data->beginScene = SDL_FALSE;
}
return 0;
}
D3D_SetBlendMode()：设置渲染器状态。
static void D3D_SetBlendMode(D3D_RenderData * data, int blendMode)
{
switch (blendMode) {
case SDL_BLENDMODE_NONE:
IDirect3DDevice9_SetRenderState(data->device, D3DRS_ALPHABLENDENABLE,
FALSE);
break;
case SDL_BLENDMODE_BLEND:
IDirect3DDevice9_SetRenderState(data->device, D3DRS_ALPHABLENDENABLE,
TRUE);
IDirect3DDevice9_SetRenderState(data->device, D3DRS_SRCBLEND,
D3DBLEND_SRCALPHA);
IDirect3DDevice9_SetRenderState(data->device, D3DRS_DESTBLEND,
D3DBLEND_INVSRCALPHA);
if (data->enableSeparateAlphaBlend) {
IDirect3DDevice9_SetRenderState(data->device, D3DRS_SRCBLENDALPHA,
D3DBLEND_ONE);
IDirect3DDevice9_SetRenderState(data->device, D3DRS_DESTBLENDALPHA,
D3DBLEND_INVSRCALPHA);
}
break;
case SDL_BLENDMODE_ADD:
IDirect3DDevice9_SetRenderState(data->device, D3DRS_ALPHABLENDENABLE,
TRUE);
IDirect3DDevice9_SetRenderState(data->device, D3DRS_SRCBLEND,
D3DBLEND_SRCALPHA);
IDirect3DDevice9_SetRenderState(data->device, D3DRS_DESTBLEND,
D3DBLEND_ONE);
if (data->enableSeparateAlphaBlend) {
IDirect3DDevice9_SetRenderState(data->device, D3DRS_SRCBLENDALPHA,
D3DBLEND_ZERO);
IDirect3DDevice9_SetRenderState(data->device, D3DRS_DESTBLENDALPHA,
D3DBLEND_ONE);
}
break;
case SDL_BLENDMODE_MOD:
IDirect3DDevice9_SetRenderState(data->device, D3DRS_ALPHABLENDENABLE,
TRUE);
IDirect3DDevice9_SetRenderState(data->device, D3DRS_SRCBLEND,
D3DBLEND_ZERO);
IDirect3DDevice9_SetRenderState(data->device, D3DRS_DESTBLEND,
D3DBLEND_SRCCOLOR);
if (data->enableSeparateAlphaBlend) {
IDirect3DDevice9_SetRenderState(data->device, D3DRS_SRCBLENDALPHA,
D3DBLEND_ZERO);
IDirect3DDevice9_SetRenderState(data->device, D3DRS_DESTBLENDALPHA,
D3DBLEND_ONE);
}
break;
}
}
D3D_UpdateTextureScaleMode()：设置纹理采样方式。
static void D3D_UpdateTextureScaleMode(D3D_RenderData *data, D3D_TextureData *texturedata, unsigned index)
{
if (texturedata->scaleMode != data->scaleMode[index]) {
IDirect3DDevice9_SetSamplerState(data->device, index, D3DSAMP_MINFILTER,
texturedata->scaleMode);
IDirect3DDevice9_SetSamplerState(data->device, index, D3DSAMP_MAGFILTER,
texturedata->scaleMode);
data->scaleMode[index] = texturedata->scaleMode;
}
}
2. OpenGL
OpenGL渲染器中对应RenderCopy()的函数是GL_RenderCopy()，它的源代码如下所示（位于render\opengl\SDL_render_gl.c）。
static int GL_RenderCopy(SDL_Renderer * renderer, SDL_Texture * texture,
const SDL_Rect * srcrect, const SDL_FRect * dstrect)
{
GL_RenderData *data = (GL_RenderData *) renderer->driverdata;
GL_TextureData *texturedata = (GL_TextureData *) texture->driverdata;
GLfloat 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(minx, miny);
data->glTexCoord2f(maxu, minv);
data->glVertex2f(maxx, miny);
data->glTexCoord2f(minu, maxv);
data->glVertex2f(minx, maxy);
data->glTexCoord2f(maxu, maxv);
data->glVertex2f(maxx, maxy);
data->glEnd();
data->glDisable(texturedata->type);
return GL_CheckError("", renderer);
}
从代码中可以看出，GL_RenderCopy()函数调用了OpenGL的API函数glActiveTexture()，glBindTexture()创建了一个纹理。并且使用GL_SetBlendMode()，GL_SetShader()设置了有关的一些参数。
有一点需要注意，在OpenGL渲染器中，如果输入像素格式是YUV，就会使用3个纹理。
3. Software
Software渲染器中对应RenderCopy()的函数是SW_RenderCopy()，它的源代码如下所示（位于render\software\SDL_render_sw.c）。
static int SW_RenderCopy(SDL_Renderer * renderer, SDL_Texture * texture,
const SDL_Rect * srcrect, const SDL_FRect * dstrect)
{
SDL_Surface *surface = SW_ActivateRenderer(renderer);
SDL_Surface *src = (SDL_Surface *) texture->driverdata;
SDL_Rect final_rect;
if (!surface) {
return -1;
}
if (renderer->viewport.x || renderer->viewport.y) {
final_rect.x = (int)(renderer->viewport.x + dstrect->x);
final_rect.y = (int)(renderer->viewport.y + dstrect->y);
} else {
final_rect.x = (int)dstrect->x;
final_rect.y = (int)dstrect->y;
}
final_rect.w = (int)dstrect->w;
final_rect.h = (int)dstrect->h;
if ( srcrect->w == final_rect.w && srcrect->h == final_rect.h ) {
return SDL_BlitSurface(src, srcrect, surface, &final_rect);
} else {
return SDL_BlitScaled(src, srcrect, surface, &final_rect);
}
}
该函数的源代码还没有详细分析。