通过cocos2d-x的CCGLProgram和CCShaderCache的实现来分析OpenGL

http://blog.csdn.net/while0/article/details/9666829

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。

[cpp] view plaincopy

1. bool CCGLProgram::initWithVertexShaderByteArray(const GLchar* vShaderByteArray, const GLchar* fShaderByteArray)  
2. {  
3.     m_uProgram = glCreateProgram(); //创建一个Program，id为m_uProgram  
4.     CHECK_GL_ERROR_DEBUG();  
5.   
6.     m_uVertShader = m_uFragShader = 0;  
7.   
8.     if (vShaderByteArray)  
9.     {  
10.         //创建顶点着色器并编译，id为m_uVertShader，vShaderByteArray是顶点着色器的源码      
11.         if (!compileShader(&m_uVertShader, GL_VERTEX_SHADER, vShaderByteArray))  
12.         {  
13.             CCLOG("cocos2d: ERROR: Failed to compile vertex shader");  
14.         }  
15.     }  
16.   
17.     // Create and compile fragment shader  
18.     if (fShaderByteArray)  
19.     {  
20.         //创建片元着色器并编译，id为m_uFragShader，fShaderByteArray是片元着色器的源码。      
21.         if (!compileShader(&m_uFragShader, GL_FRAGMENT_SHADER, fShaderByteArray))  
22.         {  
23.             CCLOG("cocos2d: ERROR: Failed to compile fragment shader");  
24.         }  
25.     }  
26.   
27.     if (m_uVertShader)  
28.     {  
29.         //绑定顶点着色器  
30.         glAttachShader(m_uProgram, m_uVertShader);  
31.     }  
32.     CHECK_GL_ERROR_DEBUG();  
33.   
34.     if (m_uFragShader)  
35.     {  
36.         //绑定片元着色器      
37.         glAttachShader(m_uProgram, m_uFragShader);  
38.     }  
39.     m_pHashForUniforms = NULL;  
40.       
41.     CHECK_GL_ERROR_DEBUG();  
42.   
43.     return true;  
44. }  
45.   
46. bool CCGLProgram::compileShader(GLuint * shader, GLenum type, const GLchar* source)  
47. {  
48.     GLint status;  
49.    
50.     if (!source)  
51.     {  
52.         return false;  
53.     }  
54.       
55.     const GLchar *sources[] = {  
56. #if (CC_TARGET_PLATFORM != CC_PLATFORM_WIN32 && CC_TARGET_PLATFORM != CC_PLATFORM_LINUX && CC_TARGET_PLATFORM != CC_PLATFORM_MAC)  
57.         (type == GL_VERTEX_SHADER ? "precision highp float;\n" : "precision mediump float;\n"),  
58. #endif  
59.         "uniform mat4 CC_PMatrix;\n"  
60.         "uniform mat4 CC_MVMatrix;\n"  
61.         "uniform mat4 CC_MVPMatrix;\n"  
62.         "uniform vec4 CC_Time;\n"  
63.         "uniform vec4 CC_SinTime;\n"  
64.         "uniform vec4 CC_CosTime;\n"  
65.         "uniform vec4 CC_Random01;\n"  
66.         "//CC INCLUDES END\n\n",  
67.         source,  
68.     };  
69.   
70.     *shader = glCreateShader(type); //创建shader  
71.     glShaderSource(*shader, sizeof(sources)/sizeof(*sources), sources, NULL);  //指定源码  
72.     glCompileShader(*shader); //编译shader  
73.   
74.     glGetShaderiv(*shader, GL_COMPILE_STATUS, &status); //获得shader编译的结果  
75.   
76.     if (! status)  //编译失败打印log  
77.     {  
78.         GLsizei length;  
79.         glGetShaderiv(*shader, GL_SHADER_SOURCE_LENGTH, &length);  
80.         GLchar* src = (GLchar *)malloc(sizeof(GLchar) * length);  
81.           
82.         glGetShaderSource(*shader, length, NULL, src);  
83.         CCLOG("cocos2d: ERROR: Failed to compile shader:\n%s", src);  
84.           
85.         if (type == GL_VERTEX_SHADER)  
86.         {  
87.             CCLOG("cocos2d: %s", vertexShaderLog());  
88.         }  
89.         else  
90.         {  
91.             CCLOG("cocos2d: %s", fragmentShaderLog());  
92.         }  
93.         free(src);  
94.   
95.         abort();  
96.     }  
97.     return (status == GL_TRUE);  
98. }  

下面是初始化Shader的过程，通过CCShaderCache::loadDefaultShaders来完成。

[cpp] view plaincopy

1. void CCShaderCache::loadDefaultShaders()  
2. {  
3.     // Position Texture Color shader  
4.     CCGLProgram *p = new CCGLProgram(); //创建CCGLProgram对象来操作OpenGL的shader  
5.     loadDefaultShader(p, kCCShaderType_PositionTextureColor); //完成该CCGLProgram对象的初始化，如shaders的创建，编译和绑定  
6.                                                               //此处创建的是顶点纹理颜色的program.  
7.   
8.     m_pPrograms->setObject(p, kCCShader_PositionTextureColor); //存入字典，key为kCCShader_PositionTextureColor  
9.     p->release();  
10.   
11.     // Position Texture Color alpha test  
12.     p = new CCGLProgram();  
13.     loadDefaultShader(p, kCCShaderType_PositionTextureColorAlphaTest);  
14.   
15.     m_pPrograms->setObject(p, kCCShader_PositionTextureColorAlphaTest);  
16.     p->release();  
17.   
18.     //  
19.     // Position, Color shader  
20.     //  
21.     p = new CCGLProgram();  
22.     loadDefaultShader(p, kCCShaderType_PositionColor);  //此处创建的是顶点颜色的program.  
23.   
24.     m_pPrograms->setObject(p, kCCShader_PositionColor);  
25.     p->release();  
26.   
27.     //  
28.     // Position Texture shader  
29.     //  
30.     p = new CCGLProgram();  
31.     loadDefaultShader(p, kCCShaderType_PositionTexture);  //此处创建的是顶点纹理的program.  
32.   
33.     m_pPrograms->setObject(p, kCCShader_PositionTexture);  
34.     p->release();  
35.   
36.     //  
37.     // Position, Texture attribs, 1 Color as uniform shader  
38.     //  
39.     p = new CCGLProgram();  
40.     loadDefaultShader(p, kCCShaderType_PositionTexture_uColor);  
41.   
42.     m_pPrograms->setObject(p ,kCCShader_PositionTexture_uColor);  
43.     p->release();  
44.   
45.     //  
46.     // Position Texture A8 Color shader  
47.     //  
48.     p = new CCGLProgram();  
49.     loadDefaultShader(p, kCCShaderType_PositionTextureA8Color);  
50.       
51.     m_pPrograms->setObject(p, kCCShader_PositionTextureA8Color);  
52.     p->release();  
53.   
54.     //  
55.     // Position and 1 color passed as a uniform (to simulate glColor4ub )  
56.     //  
57.     p = new CCGLProgram();  
58.     loadDefaultShader(p, kCCShaderType_Position_uColor);  
59.       
60.     m_pPrograms->setObject(p, kCCShader_Position_uColor);  
61.     p->release();  
62.       
63.     //  
64.     // Position, Legth(TexCoords, Color (used by Draw Node basically )  
65.     //  
66.     p = new CCGLProgram();  
67.     loadDefaultShader(p, kCCShaderType_PositionLengthTexureColor);  
68.       
69.     m_pPrograms->setObject(p, kCCShader_PositionLengthTexureColor);  
70.     p->release();  
71. }  
72.   
73. void CCShaderCache::loadDefaultShader(CCGLProgram *p, int type)  
74. {  
75.     switch (type) {  
76.         case kCCShaderType_PositionTextureColor:  
77.             //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。  
78.             p->initWithVertexShaderByteArray(ccPositionTextureColor_vert, ccPositionTextureColor_frag);  
79.               
80.             //绑定属性名称和索引，属性名称在shader源码中已经定义。  
81.             p->addAttribute(kCCAttributeNamePosition, kCCVertexAttrib_Position);  
82.             p->addAttribute(kCCAttributeNameColor, kCCVertexAttrib_Color);  
83.             p->addAttribute(kCCAttributeNameTexCoord, kCCVertexAttrib_TexCoords);  
84.               
85.             break;  
86.         case kCCShaderType_PositionTextureColorAlphaTest:  
87.             p->initWithVertexShaderByteArray(ccPositionTextureColor_vert, ccPositionTextureColorAlphaTest_frag);  
88.               
89.             p->addAttribute(kCCAttributeNamePosition, kCCVertexAttrib_Position);  
90.             p->addAttribute(kCCAttributeNameColor, kCCVertexAttrib_Color);  
91.             p->addAttribute(kCCAttributeNameTexCoord, kCCVertexAttrib_TexCoords);  
92.   
93.             break;  
94.         case kCCShaderType_PositionColor:    
95.             p->initWithVertexShaderByteArray(ccPositionColor_vert ,ccPositionColor_frag);  
96.               
97.             p->addAttribute(kCCAttributeNamePosition, kCCVertexAttrib_Position);  
98.             p->addAttribute(kCCAttributeNameColor, kCCVertexAttrib_Color);  
99.   
100.             break;  
101.         case kCCShaderType_PositionTexture:  
102.             p->initWithVertexShaderByteArray(ccPositionTexture_vert ,ccPositionTexture_frag);  
103.               
104.             p->addAttribute(kCCAttributeNamePosition, kCCVertexAttrib_Position);  
105.             p->addAttribute(kCCAttributeNameTexCoord, kCCVertexAttrib_TexCoords);  
106.   
107.             break;  
108.         case kCCShaderType_PositionTexture_uColor:  
109.             p->initWithVertexShaderByteArray(ccPositionTexture_uColor_vert, ccPositionTexture_uColor_frag);  
110.               
111.             p->addAttribute(kCCAttributeNamePosition, kCCVertexAttrib_Position);  
112.             p->addAttribute(kCCAttributeNameTexCoord, kCCVertexAttrib_TexCoords);  
113.   
114.             break;  
115.         case kCCShaderType_PositionTextureA8Color:  
116.             p->initWithVertexShaderByteArray(ccPositionTextureA8Color_vert, ccPositionTextureA8Color_frag);  
117.               
118.             p->addAttribute(kCCAttributeNamePosition, kCCVertexAttrib_Position);  
119.             p->addAttribute(kCCAttributeNameColor, kCCVertexAttrib_Color);  
120.             p->addAttribute(kCCAttributeNameTexCoord, kCCVertexAttrib_TexCoords);  
121.   
122.             break;  
123.         case kCCShaderType_Position_uColor:  
124.             p->initWithVertexShaderByteArray(ccPosition_uColor_vert, ccPosition_uColor_frag);      
125.               
126.             p->addAttribute("aVertex", kCCVertexAttrib_Position);      
127.               
128.             break;  
129.         case kCCShaderType_PositionLengthTexureColor:  
130.             p->initWithVertexShaderByteArray(ccPositionColorLengthTexture_vert, ccPositionColorLengthTexture_frag);  
131.               
132.             p->addAttribute(kCCAttributeNamePosition, kCCVertexAttrib_Position);  
133.             p->addAttribute(kCCAttributeNameTexCoord, kCCVertexAttrib_TexCoords);  
134.             p->addAttribute(kCCAttributeNameColor, kCCVertexAttrib_Color);  
135.               
136.             break;  
137.         default:  
138.             CCLOG("cocos2d: %s:%d, error shader type", __FUNCTION__, __LINE__);  
139.             return;  
140.     }  
141.       
142.     p->link(); //调用glLinkProgram链接  
143.     p->updateUniforms();  
144.       
145.     CHECK_GL_ERROR_DEBUG();  
146. }  
147.   
148. 上面创建的几种类型的program说明如下：  
149. enum {      
150.     kCCShaderType_PositionTextureColor, //顶点格式为位置+纹理UV+材质色    
151.     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    
152.     
153.     kCCShaderType_PositionColor, // 顶点格式为位置+材质色    
154.     
155.     kCCShaderType_PositionTexture, //顶点格式为位置+纹理UV     
156.     
157.     kCCShaderType_PositionTexture_uColor, //顶点格式为位置+纹理UV+材质色    
158.     
159.     kCCShaderType_PositionTextureA8Color, //顶点格式为位置+纹理UV+灰度    
160.     
161.     kCCShaderType_Position_uColor, //顶点格式为位置+材质色     
162.         
163.     kCCShaderType_MAX,  //枚举结束值    
164. };   

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：

[cpp] view plaincopy

1. "                                                   \n\  
2. attribute vec4 a_position;                          \n\  
3. attribute vec2 a_texCoord;                          \n\  
4. attribute vec4 a_color;                             \n\  
5.                                                     \n\  
6. #ifdef GL_ES                                        \n\  
7. varying lowp vec4 v_fragmentColor;                  \n\  
8. varying mediump vec2 v_texCoord;                    \n\  
9. #else                                               \n\  
10. varying vec4 v_fragmentColor;                       \n\  
11. varying vec2 v_texCoord;                            \n\  
12. #endif                                              \n\  
13.                                                     \n\  
14. void main()                                         \n\  
15. {                                                   \n\  
16.     gl_Position = CC_MVPMatrix * a_position;        \n\  
17.     v_fragmentColor = a_color;                      \n\  
18.     v_texCoord = a_texCoord;                        \n\  
19. }                                                   \n\  
20. ";  

ccShader_PositionTextureColor_frag.h内容为：

[cpp] view plaincopy

1. "                                           \n\  
2. #ifdef GL_ES                                \n\  
3. precision lowp float;                       \n\  
4. #endif                                      \n\  
5.                                             \n\  
6. varying vec4 v_fragmentColor;               \n\  
7. varying vec2 v_texCoord;                    \n\  
8. uniform sampler2D CC_Texture0;              \n\  
9.                                             \n\  
10. void main()                                 \n\  
11. {                                           \n\  
12.     gl_FragColor = v_fragmentColor * texture2D(CC_Texture0, v_texCoord);            \n\  
13. }                                           \n\  
14. ";