macos - GLSL 示例无法在 Mac 上运行

Question

我正在尝试在 Mac 上创建一个 GLSL 示例。我正在尝试为每个顶点设置一种颜色属性。但是，当程序运行时，我只是看到紫色屏幕(紫色来自 glClearColor)。我发布了相关的代码片段。

-(void)drawRect:(NSRect)dirtyRect
{    
    // get program ID for shader program
    GLuint programID = [self loadShaders];

    // get new dimensions
    NSSize dim = [self frame].size;

    // clear the background with color
    glClearColor(0.4f, 0.1f, 0.7f, 1.0f);
    glDepthRange(1.0, -1.0);
    glViewport(0, 0, dim.width, dim.height);
    glClear(GL_COLOR_BUFFER_BIT);

    // generate a buffer for our triangle
    glGenBuffers(2, vertexBuffer);

    glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer[0]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
    glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer[1]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(colors), colors, GL_STATIC_DRAW);

    glUseProgram(programID);

    glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer[0]);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(VERTEX_POS_INDEX, VERTEX_POS_SIZE, GL_FLOAT, GL_FALSE, VERTEX_POS_SIZE*sizeof(vertices), vertices);

    glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer[1]);
    glEnableVertexAttribArray(1);
    glVertexAttribPointer(VERTEX_COLOR_INDEX, VERTEX_COLOR_SIZE, GL_FLOAT, GL_FALSE, VERTEX_POS_SIZE*sizeof(colors), colors);

    glDrawArrays(GL_TRIANGLES, 0, 3);

    glDisableVertexAttribArray(0);
    glDisableVertexAttribArray(1);
    glUseProgram(0);

    // flush buffer
    glFlush();
    [[self openGLContext] flushBuffer];
}

然后是加载阴影代码:

-(GLuint)loadShaders
{
    printf("GLSL version %s\n", glGetString(GL_SHADING_LANGUAGE_VERSION));
    printf("GL Version: %s", glGetString(GL_VERSION));

    // Create the shaders
    GLuint vertexShaderID = glCreateShader(GL_VERTEX_SHADER);
    GLuint fragmentShaderID = glCreateShader(GL_FRAGMENT_SHADER);

    // get handle for app bundle
    NSBundle *appBundle = [NSBundle mainBundle];

    // get the path for the vertex shader file
    NSString *vertexFilePath = [appBundle pathForResource:vertexShaderFile ofType:nil];
    // get the path for the fragment shader file
    NSString *fragmentFilePath = [appBundle pathForResource:fragmentShaderFile ofType:nil];

    // get the contents of the vertex shader file into a string
    NSString *vertexFileContents = [NSString stringWithContentsOfFile:vertexFilePath encoding:NSUTF8StringEncoding error:NULL];
    NSLog(@"%@", vertexFileContents);
    // get the contents of the fragment shader file into a string
    NSString *fragmentFileContents = [NSString stringWithContentsOfFile:fragmentFilePath encoding:NSUTF8StringEncoding error:NULL];
    NSLog(@"%@", fragmentFileContents);

    GLint Result = GL_FALSE;
    int infoLogLength;

    // get a pointer the vertex shader program source, compile shader program
    const char *vertexSourcePointer = [vertexFileContents UTF8String];
    glShaderSource(vertexShaderID, 1, &vertexSourcePointer, NULL);
    glCompileShader(vertexShaderID);
    // check the vertex shader
    glGetShaderiv(vertexShaderID, GL_COMPILE_STATUS, &Result);
    glGetShaderiv(vertexShaderID, GL_INFO_LOG_LENGTH, &infoLogLength);
    char vertexShaderErrorMessage[infoLogLength];
    glGetShaderInfoLog(vertexShaderID, infoLogLength, NULL, vertexShaderErrorMessage);
    // print error message
    NSLog(@"%@", [NSString stringWithUTF8String:vertexShaderErrorMessage]);

    // get a pointer to the fragment shader program source, compile shader program
    const char *fragmentSourcePointer = [fragmentFileContents UTF8String];
    glShaderSource(fragmentShaderID, 1, &fragmentSourcePointer, NULL);
    glCompileShader(fragmentShaderID);
    // check the fragment shader
    glGetShaderiv(fragmentShaderID, GL_COMPILE_STATUS, &Result);
    glGetShaderiv(fragmentShaderID, GL_INFO_LOG_LENGTH, &infoLogLength);
    char fragmentShaderErrorMessage[infoLogLength];
    glGetShaderInfoLog(fragmentShaderID, infoLogLength, NULL, fragmentShaderErrorMessage);
    // print error message
    NSLog(@"%@", [NSString stringWithUTF8String:fragmentShaderErrorMessage]);

    // link the program
    NSLog(@"Linking program...");
    GLuint programID = glCreateProgram();
    glAttachShader(programID, vertexShaderID);
    glAttachShader(programID, fragmentShaderID);

    glBindAttribLocation(programID, 0, "position");
    glBindAttribLocation(programID, 1, "inColor");

    glLinkProgram(programID);

    // check the program
    glGetProgramiv(programID, GL_LINK_STATUS, &Result);
    glGetProgramiv(programID, GL_INFO_LOG_LENGTH, &infoLogLength);
    char shaderProgramErrorMessage[max(infoLogLength, (int)1)];
    glGetProgramInfoLog(programID, infoLogLength, NULL, shaderProgramErrorMessage);
    // pring error message
    NSLog(@"%@", [NSString stringWithUTF8String:shaderProgramErrorMessage]);

    // delete shaders
    glDeleteShader(vertexShaderID);
    glDeleteShader(fragmentShaderID);

    return programID;

}

最后是着色器:

#version 120

attribute vec4 position;
attribute vec4 inColor;
varying vec4 outColor;
void main()
{
    gl_Position = position;
    outColor = inColor;
}

和

#version 120

varying vec4 outColor;
void main()
{
    gl_FragColor = outColor;
}

Answer 1

看起来相当不错，但我确实发现了一个错误。

glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer[0]);
glEnableVertexAttribArray(0);
glVertexAttribPointer(VERTEX_POS_INDEX, 
                      VERTEX_POS_SIZE, 
                      GL_FLOAT, 
                      GL_FALSE, 
                      VERTEX_POS_SIZE*sizeof(vertices), 
                      vertices);

如果您使用的是 VBO，则 glVertexAttribPointer 的最终属性应该是距当前绑定(bind)缓冲区开头的偏移。

如果您使用顶点数组(无 glBindBuffer)，那么您将使用 glVertexAttribPointer 的最后一个参数指向顶点。

但是，由于您已经将顶点上传到缓冲区并将其绑定(bind)，因此 glVertexAttribPointer 的最终值应该是距顶点缓冲区开头的偏移，在你的情况下，应该是0。

颜色缓冲区也有同样的错误。