通过cocos2d-x的CCGLProgram和CCShaderCache的实现来分析OpenGL ES中的Shader编程
在OpenGL ES中，Shader是着色器，包括两种：顶点着色器（Vertex Shader）和片元着色器（Fragment Shader）。每个program对象有且仅有一个Vertex Shader对象和一个Fragment Shader对象连接到它。
Shader和Program编程步骤：
1. 创建Shader
1）编写Vertex Shader和Fragment Shader源码。
2）创建两个shader 实例：GLuint glCreateShader(GLenum type);
3）给Shader实例指定源码。 glShaderSource
4）在线编译shaer源码 void glCompileShader(GLuint shader)
2. 创建Program
1）创建program GLuint glCreateProgram(void)
2）绑定shader到program 。 void glAttachShader(GLuint program, GLuint shader)。每个program必须绑定一个Vertex Shader 和一个Fragment Shader。
3）链接program 。 void glLinkProgram(GLuint program)
4）使用porgram 。 void glUseProgram(GLuint program)
在cocos2d-x中使用两个类CCGLProgram和CCShaderCache来完成这些操作，其中CCGLProgram类是基本类，封装了对OpenGL ES接口的调用，而CCShaderCache通过CCGLProgram来完成对shaders的缓存和管理。
bool CCGLProgram::initWithVertexShaderByteArray(const GLchar* vShaderByteArray, const GLchar* fShaderByteArray)
{
m_uProgram = glCreateProgram(); //创建一个Program，id为m_uProgram
CHECK_GL_ERROR_DEBUG();
m_uVertShader = m_uFragShader = 0;
if (vShaderByteArray)
{
//创建顶点着色器并编译，id为m_uVertShader，vShaderByteArray是顶点着色器的源码
if (!compileShader(&m_uVertShader, GL_VERTEX_SHADER, vShaderByteArray))
{
CCLOG("cocos2d: ERROR: Failed to compile vertex shader");
}
}
// Create and compile fragment shader
if (fShaderByteArray)
{
//创建片元着色器并编译，id为m_uFragShader，fShaderByteArray是片元着色器的源码。
if (!compileShader(&m_uFragShader, GL_FRAGMENT_SHADER, fShaderByteArray))
{
CCLOG("cocos2d: ERROR: Failed to compile fragment shader");
}
}
if (m_uVertShader)
{
//绑定顶点着色器
glAttachShader(m_uProgram, m_uVertShader);
}
CHECK_GL_ERROR_DEBUG();
if (m_uFragShader)
{
//绑定片元着色器
glAttachShader(m_uProgram, m_uFragShader);
}
m_pHashForUniforms = NULL;
CHECK_GL_ERROR_DEBUG();
return true;
}
bool CCGLProgram::compileShader(GLuint * shader, GLenum type, const GLchar* source)
{
GLint status;
if (!source)
{
return false;
}
const GLchar *sources[] = {
#if (CC_TARGET_PLATFORM != CC_PLATFORM_WIN32 && CC_TARGET_PLATFORM != CC_PLATFORM_LINUX && CC_TARGET_PLATFORM != CC_PLATFORM_MAC)
(type == GL_VERTEX_SHADER ? "precision highp float;\n" : "precision mediump float;\n"),
#endif
"uniform mat4 CC_PMatrix;\n"
"uniform mat4 CC_MVMatrix;\n"
"uniform mat4 CC_MVPMatrix;\n"
"uniform vec4 CC_Time;\n"
"uniform vec4 CC_SinTime;\n"
"uniform vec4 CC_CosTime;\n"
"uniform vec4 CC_Random01;\n"
"//CC INCLUDES END\n\n",
source,
};
*shader = glCreateShader(type); //创建shader
glShaderSource(*shader, sizeof(sources)/sizeof(*sources), sources, NULL); //指定源码
glCompileShader(*shader); //编译shader
glGetShaderiv(*shader, GL_COMPILE_STATUS, &status); //获得shader编译的结果
if (! status) //编译失败打印log
{
GLsizei length;
glGetShaderiv(*shader, GL_SHADER_SOURCE_LENGTH, &length);
GLchar* src = (GLchar *)malloc(sizeof(GLchar) * length);
glGetShaderSource(*shader, length, NULL, src);
CCLOG("cocos2d: ERROR: Failed to compile shader:\n%s", src);
if (type == GL_VERTEX_SHADER)
{
CCLOG("cocos2d: %s", vertexShaderLog());
}
else
{
CCLOG("cocos2d: %s", fragmentShaderLog());
}
free(src);
abort();
}
return (status == GL_TRUE);
}
下面是初始化Shader的过程，通过CCShaderCache::loadDefaultShaders来完成。
void CCShaderCache::loadDefaultShaders()
{
// Position Texture Color shader
CCGLProgram *p = new CCGLProgram(); //创建CCGLProgram对象来操作OpenGL的shader
loadDefaultShader(p, kCCShaderType_PositionTextureColor); //完成该CCGLProgram对象的初始化，如shaders的创建，编译和绑定
//此处创建的是顶点纹理颜色的program.
m_pPrograms->setObject(p, kCCShader_PositionTextureColor); //存入字典，key为kCCShader_PositionTextureColor
p->release();
// Position Texture Color alpha test
p = new CCGLProgram();
loadDefaultShader(p, kCCShaderType_PositionTextureColorAlphaTest);
m_pPrograms->setObject(p, kCCShader_PositionTextureColorAlphaTest);
p->release();
//
// Position, Color shader
//
p = new CCGLProgram();
loadDefaultShader(p, kCCShaderType_PositionColor); //此处创建的是顶点颜色的program.
m_pPrograms->setObject(p, kCCShader_PositionColor);
p->release();
//
// Position Texture shader
//
p = new CCGLProgram();
loadDefaultShader(p, kCCShaderType_PositionTexture); //此处创建的是顶点纹理的program.
m_pPrograms->setObject(p, kCCShader_PositionTexture);
p->release();
//
// Position, Texture attribs, 1 Color as uniform shader
//
p = new CCGLProgram();
loadDefaultShader(p, kCCShaderType_PositionTexture_uColor);
m_pPrograms->setObject(p ,kCCShader_PositionTexture_uColor);
p->release();
//
// Position Texture A8 Color shader
//
p = new CCGLProgram();
loadDefaultShader(p, kCCShaderType_PositionTextureA8Color);
m_pPrograms->setObject(p, kCCShader_PositionTextureA8Color);
p->release();
//
// Position and 1 color passed as a uniform (to simulate glColor4ub )
//
p = new CCGLProgram();
loadDefaultShader(p, kCCShaderType_Position_uColor);
m_pPrograms->setObject(p, kCCShader_Position_uColor);
p->release();
//
// Position, Legth(TexCoords, Color (used by Draw Node basically )
//
p = new CCGLProgram();
loadDefaultShader(p, kCCShaderType_PositionLengthTexureColor);
m_pPrograms->setObject(p, kCCShader_PositionLengthTexureColor);
p->release();
}
void CCShaderCache::loadDefaultShader(CCGLProgram *p, int type)
{
switch (type) {
case kCCShaderType_PositionTextureColor:
//shaders的创建，编译和绑定，不同的program的顶点着色源码和片元着色源码不同。
p->initWithVertexShaderByteArray(ccPositionTextureColor_vert, ccPositionTextureColor_frag);
//绑定属性名称和索引，属性名称在shader源码中已经定义。
p->addAttribute(kCCAttributeNamePosition, kCCVertexAttrib_Position);
p->addAttribute(kCCAttributeNameColor, kCCVertexAttrib_Color);
p->addAttribute(kCCAttributeNameTexCoord, kCCVertexAttrib_TexCoords);
break;
case kCCShaderType_PositionTextureColorAlphaTest:
p->initWithVertexShaderByteArray(ccPositionTextureColor_vert, ccPositionTextureColorAlphaTest_frag);
p->addAttribute(kCCAttributeNamePosition, kCCVertexAttrib_Position);
p->addAttribute(kCCAttributeNameColor, kCCVertexAttrib_Color);
p->addAttribute(kCCAttributeNameTexCoord, kCCVertexAttrib_TexCoords);
break;
case kCCShaderType_PositionColor:
p->initWithVertexShaderByteArray(ccPositionColor_vert ,ccPositionColor_frag);
p->addAttribute(kCCAttributeNamePosition, kCCVertexAttrib_Position);
p->addAttribute(kCCAttributeNameColor, kCCVertexAttrib_Color);
break;
case kCCShaderType_PositionTexture:
p->initWithVertexShaderByteArray(ccPositionTexture_vert ,ccPositionTexture_frag);
p->addAttribute(kCCAttributeNamePosition, kCCVertexAttrib_Position);
p->addAttribute(kCCAttributeNameTexCoord, kCCVertexAttrib_TexCoords);
break;
case kCCShaderType_PositionTexture_uColor:
p->initWithVertexShaderByteArray(ccPositionTexture_uColor_vert, ccPositionTexture_uColor_frag);
p->addAttribute(kCCAttributeNamePosition, kCCVertexAttrib_Position);
p->addAttribute(kCCAttributeNameTexCoord, kCCVertexAttrib_TexCoords);
break;
case kCCShaderType_PositionTextureA8Color:
p->initWithVertexShaderByteArray(ccPositionTextureA8Color_vert, ccPositionTextureA8Color_frag);
p->addAttribute(kCCAttributeNamePosition, kCCVertexAttrib_Position);
p->addAttribute(kCCAttributeNameColor, kCCVertexAttrib_Color);
p->addAttribute(kCCAttributeNameTexCoord, kCCVertexAttrib_TexCoords);
break;
case kCCShaderType_Position_uColor:
p->initWithVertexShaderByteArray(ccPosition_uColor_vert, ccPosition_uColor_frag);
p->addAttribute("aVertex", kCCVertexAttrib_Position);
break;
case kCCShaderType_PositionLengthTexureColor:
p->initWithVertexShaderByteArray(ccPositionColorLengthTexture_vert, ccPositionColorLengthTexture_frag);
p->addAttribute(kCCAttributeNamePosition, kCCVertexAttrib_Position);
p->addAttribute(kCCAttributeNameTexCoord, kCCVertexAttrib_TexCoords);
p->addAttribute(kCCAttributeNameColor, kCCVertexAttrib_Color);
break;
default:
CCLOG("cocos2d: %s:%d, error shader type", __FUNCTION__, __LINE__);
return;
}
p->link(); //调用glLinkProgram链接
p->updateUniforms();
CHECK_GL_ERROR_DEBUG();
}
上面创建的几种类型的program说明如下：
enum {
kCCShaderType_PositionTextureColor, //顶点格式为位置+纹理UV+材质色
kCCShaderType_PositionTextureColorAlphaTest, //顶点格式为顶点格式为位置+纹理UV+材质色+用于AlphaTest的ALPHA值
kCCShaderType_PositionColor, // 顶点格式为位置+材质色
kCCShaderType_PositionTexture, //顶点格式为位置+纹理UV
kCCShaderType_PositionTexture_uColor, //顶点格式为位置+纹理UV+材质色
kCCShaderType_PositionTextureA8Color, //顶点格式为位置+纹理UV+灰度
kCCShaderType_Position_uColor, //顶点格式为位置+材质色
kCCShaderType_MAX, //枚举结束值
};
以类型为kCCShaderType_PositionTextureColor的program为例，它的顶点着色源码和片元着色源码分别为ccShader_PositionTextureColor_vert.h和
ccShader_PositionTextureColor_frag.h。
ccShader_PositionTextureColor_vert.h内容为：
" \n\
attribute vec4 a_position; \n\
attribute vec2 a_texCoord; \n\
attribute vec4 a_color; \n\
\n\
#ifdef GL_ES \n\
varying lowp vec4 v_fragmentColor; \n\
varying mediump vec2 v_texCoord; \n\
#else \n\
varying vec4 v_fragmentColor; \n\
varying vec2 v_texCoord; \n\
#endif \n\
\n\
void main() \n\
{ \n\
gl_Position = CC_MVPMatrix * a_position; \n\
v_fragmentColor = a_color; \n\
v_texCoord = a_texCoord; \n\
} \n\
";
ccShader_PositionTextureColor_frag.h内容为：
" \n\
#ifdef GL_ES \n\
precision lowp float; \n\
#endif \n\
\n\
varying vec4 v_fragmentColor; \n\
varying vec2 v_texCoord; \n\
uniform sampler2D CC_Texture0; \n\
\n\
void main() \n\
{ \n\
gl_FragColor = v_fragmentColor * texture2D(CC_Texture0, v_texCoord); \n\
} \n\
";