OpenGL基础探究

GLuint vertShader, fragShader;
    NSURL *vertShaderURL, *fragShaderURL;
    
    
    self.program = glCreateProgram();
    
    // Create and compile the vertex shader.
    vertShaderURL = [[NSBundle mainBundle] URLForResource:@"Shader" withExtension:@"vsh"];
    if (![self compileShader:&vertShader type:GL_VERTEX_SHADER URL:vertShaderURL]) {
        NSLog(@"Failed to compile vertex shader");
        return NO;
    }
    
    // Create and compile fragment shader.
    fragShaderURL = [[NSBundle mainBundle] URLForResource:@"Shader" withExtension:@"fsh"];
    if (![self compileShader:&fragShader type:GL_FRAGMENT_SHADER URL:fragShaderURL]) {
        NSLog(@"Failed to compile fragment shader");
        return NO;
    }
    
    // Attach vertex shader to program.
    glAttachShader(self.program, vertShader);
    
    // Attach fragment shader to program.
    glAttachShader(self.program, fragShader);
    
    // Bind attribute locations. This needs to be done prior to linking.
    glBindAttribLocation(self.program, ATTRIB_VERTEX, "position");
    glBindAttribLocation(self.program, ATTRIB_TEXCOORD, "texCoord");

首先翻译一下得出两个关键词：点、面

生成一个OpenGL程序需要两个函数

varying highp vec2 texCoordVarying;
precision mediump float;

uniform sampler2D SamplerY;
uniform sampler2D SamplerUV;
uniform mat3 colorConversionMatrix;

void main()
{
    mediump vec3 yuv;
    lowp vec3 rgb;
    
    // Subtract constants to map the video range start at 0
    yuv.x = (texture2D(SamplerY, texCoordVarying).r);// - (16.0/255.0));
    yuv.yz = (texture2D(SamplerUV, texCoordVarying).ra - vec2(0.5, 0.5));
    
    rgb = colorConversionMatrix * yuv;

    gl_FragColor = vec4(rgb,1);
//    gl_FragColor = vec4(1, 0, 0, 1);
}

shader.fsh

attribute vec4 position;
attribute vec2 texCoord;

uniform float preferredRotation;
uniform mat4 projectionMatrix;
uniform mat4 modelViewMatrix;

varying vec2 texCoordVarying;

void main()
{
    mat4 rotationMatrix = mat4( cos(preferredRotation), -sin(preferredRotation), 0.0, 0.0,
                               sin(preferredRotation),  cos(preferredRotation), 0.0, 0.0,
                               0.0,                        0.0, 1.0, 0.0,
                               0.0,                        0.0, 0.0, 1.0);
    gl_Position = projectionMatrix * modelViewMatrix * rotationMatrix * position;// * modelViewMatrix * projectionMatrix;
    texCoordVarying = texCoord;
}

shader.vsh

这两个函数中有varying或varying标明的两个同名属性字段，测试结果是必须同名而且是两个函数之间互通使用的

 在main函数上方设定的额参数，均是后面添加设定的参数，设置方法有：

在OpenGL ES中，uniform的位置不是固定的，必须在Program link完成之后才能够获得：
/ Get uniform locations.
    uniforms[UNIFORM_Y] = glGetUniformLocation(self.program, "SamplerY");
    uniforms[UNIFORM_UV] = glGetUniformLocation(self.program, "SamplerUV");
    uniforms[UNIFORM_ROTATE] = glGetUniformLocation(self.program, "preferredRotation");
    uniforms[UNIFORM_COLOR_CONVERSION_MATRIX] = glGetUniformLocation(self.program, "colorConversionMatrix");
    uniforms[UNIFORM_PROJECTION_MARTRIX] = glGetUniformLocation(self.program, "projectionMatrix");
    uniforms[UNIFORM_MODELVIEW_MARTRIX] = glGetUniformLocation(self.program, "modelViewMatrix");


/Set uniform
glUniform1i(uniforms[UNIFORM_Y], 0);
    glUniform1i(uniforms[UNIFORM_UV], 1);
    glUniform1f(uniforms[UNIFORM_ROTATE], GLKMathDegreesToRadians(180));


// Bind attribute locations. This needs to be done prior to linking.
    glBindAttribLocation(self.program, ATTRIB_VERTEX, "position");
    glBindAttribLocation(self.program, ATTRIB_TEXCOORD, "texCoord");

 //初始化纹理数据

glGenBuffers(1, &_textureBuffer);

glBindBuffer(GL_ARRAY_BUFFER, _textureBuffer);

glBufferData(GL_ARRAY_BUFFER, sizeof(sphereTexCoords), sphereTexCoords, GL_STATIC_DRAW);

//启用纹理数据

glBindBuffer(GL_ARRAY_BUFFER, _textureBuffer);

glVertexAttribPointer(ATTRIB_TEXCOORD, 2, GL_FLOAT, GL_FALSE, 0, NULL);

glEnableVertexAttribArray(ATTRIB_TEXCOORD);

glVertexAttribPointer (GLuint indx, GLint size, GLenum type, GLboolean normalized, GLsizei stride, const GLvoid* ptr)

glVertexAttribPointer(取值纹理对象, 每次取值数目, 取值类型, GL_FALSE, 间隔大小,开始取值位置);

变量赋值

三个可以赋值给我们的变量的标签

• Uniforms：在渲染循环里作为不变的输入值
• Attributes：随顶点位置不同会变的输入值
• Varyings：用来在Vertex shader和Fragment shader之间传递信息的，比如在Vertex shader中写入varying值，然后就可以在Fragment shader中读取和处理

向量

有很多种向量，但是有三种会经常看到

• vec2：两个浮点数，适合在Fragment shader中保存X和Y坐标的情况
• vec3：三个浮点数
• vec4：四个浮点数，在图像处理中持续追踪每个像素的R,G,V,A这四个值。

矩阵

是浮点数组的数组。三个经常处理的矩阵对象

• mat2：相当于保存了两个vec2对象的值或四个浮点数。
• mat3
• mat4

作者：星光社的戴铭
链接：https://www.jianshu.com/p/8687a040eb48