First knowledge of OpenGL (4) link shader

1. Shader program

Shader program object (Shader Program Object) It's the version after merging multiple shaders and finally linking them . If we want to use the shaders just compiled, we must link them (Link) For a shader program object , Then activate the shader program when rendering the object . Shaders that have activated the shader program will be used when we send rendering calls .

When linking shaders to a program , It links the output of each shader to the input of the next shader . When the output and input don't match , You will get a connection error .

step1. Create shader program object

glCreateProgram Function to create a program , And returns the name of the newly created program object ID quote .

unsigned int shaderProgram;
shaderProgram = glCreateProgram();

step2. Attach the previously compiled shader to the program object , And then use glLinkProgram Link them

glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);
glLinkProgram(shaderProgram);

step3. Failed to detect whether the linked shader program , And get the corresponding log .

Different from before , We won't call glGetShaderiv and glGetShaderInfoLog

glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
if(!success) {
    
    glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
    ...
}

step4. Activate this program object

call glUseProgram function , Use the newly created program object as its parameter .

glUseProgram(shaderProgram);

stay glUseProgram After the function call , Each shader call and rendering call uses this program object （ That is, the shader written before ) 了 .

step5. Delete shader object

glDeleteShader(vertexShader);
glDeleteShader(fragmentShader);

Now? , We have sent the input vertex data to GPU, And indicated GPU How to handle it in vertex and clip shaders . It's almost finished , But it's not over yet ,OpenGL I don't know how it interprets vertex data in memory , And how it links vertex data to the attributes of the vertex shader . The next step is to tell OpenGL How do you do it? .