Open GL ES，多个着色器

Question

我很好奇在Open GL ES 2.0程序中是否可以有多个着色器。

这是我的着色器代码。但是，attributes和uniforms仅从rigid.vert和rigid.frag着色器检索变量：

- (BOOL)loadShaders
{
GLuint rigidVertShader, rigidFragShader, skinningVertShader, skinningFragShader;
NSString *rigidVertShaderPathname, *rigidFragShaderPathname, *skinningVertShaderPathname, *skinningFragShaderPathname;

// Create shader program.
_program = glCreateProgram();

// Create and compile rigid vertex shader.
rigidVertShaderPathname = [[NSBundle mainBundle] pathForResource:@"rigid" ofType:@"vert"];
if (![self compileShader:&rigidVertShader type:GL_VERTEX_SHADER file:rigidVertShaderPathname]) {
    NSLog(@"Failed to compile rigid vertex shader");
    return NO;
}

// Create and compile rigid fragment shader.
rigidFragShaderPathname = [[NSBundle mainBundle] pathForResource:@"rigid" ofType:@"frag"];
if (![self compileShader:&rigidFragShader type:GL_FRAGMENT_SHADER file:rigidFragShaderPathname]) {
    NSLog(@"Failed to compile rigid fragment shader");
    return NO;
}

// Create and compile skinning vertex shader.
skinningVertShaderPathname = [[NSBundle mainBundle] pathForResource:@"skinning" ofType:@"vert"];
if (![self compileShader:&skinningVertShader type:GL_VERTEX_SHADER file:skinningVertShaderPathname]) {
    NSLog(@"Failed to compile skinning vertex shader");
    return NO;
}

// Create and compile skinning fragment shader.
skinningFragShaderPathname = [[NSBundle mainBundle] pathForResource:@"skinning" ofType:@"frag"];
if (![self compileShader:&skinningFragShader type:GL_FRAGMENT_SHADER file:skinningFragShaderPathname]) {
    NSLog(@"Failed to compile skinning fragment shader");
    return NO;
}

// Attach rigid vertex shader to program.
glAttachShader(_program, rigidVertShader);

// Attach rigid fragment shader to program.
glAttachShader(_program, rigidFragShader);

// Attach skinning vertex shader to program.
glAttachShader(_program, skinningVertShader);

// Attach skinning fragment shader to program.
glAttachShader(_program, skinningFragShader);

// Link program.
if (![self linkProgram:_program]) {
    NSLog(@"Failed to link program: %d", _program);

    if (rigidVertShader) {
        glDeleteShader(rigidVertShader);
        rigidVertShader = 0;
    }
    if (rigidFragShader) {
        glDeleteShader(rigidFragShader);
        rigidFragShader = 0;
    }
    if (skinningVertShader) {
        glDeleteShader(skinningVertShader);
        skinningVertShader = 0;
    }
    if (skinningFragShader) {
        glDeleteShader(skinningFragShader);
        skinningFragShader = 0;
    }
    if (_program) {
        glDeleteProgram(_program);
        _program = 0;
    }

    return NO;
}

// GET UNIFORM LOCATIONS
// Dictionary to store each active uniform
NSMutableDictionary *m_uniforms = [[NSMutableDictionary alloc] init];
int m_nUniforms = -1;
glGetProgramiv( _program, GL_ACTIVE_UNIFORMS, &m_nUniforms );

for(GLuint i = 0; i < m_nUniforms; i++)  {
    int name_len=-1, num=-1;
    GLenum type = GL_ZERO;
    char uniformName[100];

    glGetActiveUniform( _program, i, sizeof(uniformName)-1, &name_len, &num, &type, uniformName );

    uniformName[name_len] = 0;

    GLuint uniform = glGetUniformLocation( _program, uniformName );

    [m_uniforms setObject:[NSNumber numberWithUnsignedInt:uniform]
                   forKey:[NSString stringWithUTF8String:uniformName]];    
}

// GET ATTRIBUTE LOCATIONS
// Dictionary to store each active attribute
NSMutableDictionary *m_attributes = [[NSMutableDictionary alloc] init];
int m_nAttributes = -1;
glGetProgramiv( _program, GL_ACTIVE_ATTRIBUTES, &m_nAttributes );

for(GLuint i = 0; i < m_nAttributes; i++)  {
    int name_len=-1, num=-1;
    GLenum type = GL_ZERO;
    char attributesName[100];

    glGetActiveAttrib( _program, i, sizeof(attributesName)-1, &name_len, &num, &type, attributesName );

    attributesName[name_len] = 0;

    GLuint attributes = glGetAttribLocation( _program, attributesName );

    [m_attributes setObject:[NSNumber numberWithUnsignedInt:attributes]
                     forKey:[NSString stringWithUTF8String:attributesName]];
}


// Release vertex and fragment shaders.
if (rigidVertShader) {
    glDetachShader(_program, rigidVertShader);
    glDeleteShader(rigidVertShader);
}
if (rigidFragShader) {
    glDetachShader(_program, rigidFragShader);
    glDeleteShader(rigidFragShader);
}
if (skinningVertShader) {
    glDetachShader(_program, skinningVertShader);
    glDeleteShader(skinningVertShader);
}
if (skinningFragShader) {
    glDetachShader(_program, skinningFragShader);
    glDeleteShader(skinningFragShader);
}

return YES;
}

Answer 1

OpenGL ES不允许在程序unlike "desktop" OpenGL中使用同一类型的多个着色器(但它只允许声明公共函数/变量，因此它与连接着色器源代码大致相同)。从glAttachShader() spec

同一类型的多个着色器对象不能附加到单个程序对象。

..。

错误

...如果着色器已附加到程序，或者与着色器类型相同的另一个着色器对象已附加到程序，则会生成GL_INVALID_OPERATION。

我强烈怀疑对glAttachShader()的第三次和第四次调用设置了GL_INVALID_OPERATION。

检查你的错误！我在循环中调用glGetError()，直到它返回GL_NO_ERROR。

Answer 2

在OpenGL ES中，每个着色器程序只能使用一个片段和一个顶点着色器。否则它就不会起作用。