6.OpenGL学习笔记 - iOS上画三角形(不用GLKit框架)

最新推荐文章于 2019-07-21 19:00:25 发布

whoyouare888

最新推荐文章于 2019-07-21 19:00:25 发布

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分类专栏： OpenGL

本文链接：https://blog.youkuaiyun.com/whoyouare888/article/details/96346065

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本文介绍如何使用OpenGL ES通过顶点着色器和片段着色器来绘制一个简单的三角形。包括着色器的编写、编译链接以及顶点数据的设置等关键步骤。

顶点着色器：

#version 300 es
precision highp float;
layout (location = 0) in vec3 aPos;

void main()
{
    gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);
}

片段着色器：

#version 300 es
precision highp float;

out vec4 FragColor;

void main()
{
    FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);
}

编译链接两个着色器：


- (GLuint)compileShaders:(NSString *)shaderVertex shaderFragment:(NSString *)shaderFragment {
    // 1 vertex和fragment两个shader都要编译
    GLuint vertexShader = [self compileShader:shaderVertex withType:GL_VERTEX_SHADER];
    GLuint fragmentShader = [self compileShader:shaderFragment withType:GL_FRAGMENT_SHADER];
    
    // 2 连接vertex和fragment shader成一个完整的program
    GLuint glProgram = glCreateProgram();
    glAttachShader(glProgram, vertexShader);
    glAttachShader(glProgram, fragmentShader);
    
    // link program
    glLinkProgram(glProgram);
    
    // 3 check link status
    GLint linkSuccess;
    glGetProgramiv(glProgram, GL_LINK_STATUS, &linkSuccess);
    if (linkSuccess == GL_FALSE) {
        GLchar messages[256];
        glGetProgramInfoLog(glProgram, sizeof(messages), 0, &messages[0]);
        NSString *messageString = [NSString stringWithUTF8String:messages];
        NSLog(@"%@", messageString);
        exit(1);
    }
    
    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);
    
    return glProgram;
}

- (GLuint)compileShader:(NSString*)shaderName withType:(GLenum)shaderType {
    // 1 查找shader文件
    NSString* shaderPath = [[NSBundle mainBundle] pathForResource:shaderName ofType:nil];
    NSError* error;
    NSString* shaderString = [NSString stringWithContentsOfFile:shaderPath encoding:NSUTF8StringEncoding error:&error];
    if (!shaderString) {
        NSLog(@"Error loading shader: %@", error.localizedDescription);
        exit(1);
    }
    
    // 2 创建一个代表shader的OpenGL对象, 指定vertex或fragment shader
    GLuint shaderHandle = glCreateShader(shaderType);
    
    // 3 获取shader的source
    const char* shaderStringUTF8 = [shaderString UTF8String];
    int shaderStringLength = (int)[shaderString length];
    glShaderSource(shaderHandle, 1, &shaderStringUTF8, &shaderStringLength);
    
    // 4 编译shader
    glCompileShader(shaderHandle);
    
    // 5 查询shader对象的信息
    GLint compileSuccess;
    glGetShaderiv(shaderHandle, GL_COMPILE_STATUS, &compileSuccess);
    if (compileSuccess == GL_FALSE) {
        GLchar messages[256];
        glGetShaderInfoLog(shaderHandle, sizeof(messages), 0, &messages[0]);
        NSString *messageString = [NSString stringWithUTF8String:messages];
        NSLog(@"%@", messageString);
        exit(1);
    }
    
    return shaderHandle;
}

绘制三角形：

- (void)draw
{
    
    glViewport(0, 0, self.frame.size.width, self.frame.size.height);

    float vertices[] = {
        -0.5f, -0.5f, 0.0f,
        0.5f, -0.5f, 0.0f,
        0.0f,  0.5f, 0.0f
    };
    
    //顶点数据缓存
    _program = [self compileShaders:@"vertex.vsh" shaderFragment:@"fragment.fsh"];
    glUseProgram(_program);
    
    GLuint _positionSlot = glGetAttribLocation(_program, "aPos");
    glVertexAttribPointer(_positionSlot, 3, GL_FLOAT, GL_FALSE, 0, vertices);
    glEnableVertexAttribArray(_positionSlot);

    glDrawArrays(GL_TRIANGLES, 0, 3);

    [_eaglContext presentRenderbuffer:GL_RENDERBUFFER];


}

glVertexAttribPointer函数倒数第二个参数指的是跨度，传0表示紧密排列。最后一个参数表示数据源。

下载地址：

https://github.com/whoyouare888/Note/tree/master/OpenGL/OpenGL%20ES%20%E6%90%AD%E5%BB%BA%E7%8E%AF%E5%A2%83