OpenGL learning notes

Current learning status ：day01

Hello triangle

Chinese Course https://learnopengl-cn.github.io/
course http://www.opengl-tutorial.org/cn/beginners-tutorials/tutorial-1-opening-a-window/
Course source code https://github.com/opengl-tutorials/ogl/archive/master.zip

Vertex array object ：Vertex Array Object,VAO
Vertex buffer object ：Vertex Buffer Object,VBO
Index buffer object ：Element Buffer Object,EBO or Index Buffer Object,IBO

Graphics rendering pipeline ： It can be divided into two main parts ： The first part is to put your 3D The coordinates are converted to 2D coordinate , The second part is to put 2D Coordinates change to actual colored pixels .

Schematic diagram of each stage of graphic rendering pipeline ：

The blue part represents the part where we can inject custom shaders . but Most of the time , Just configure vertex and fragment shaders , But you must also define at least one vertex shader and one fragment shader （ because GPU There is no default vertex in / Fragment Shader ）.

Vertex Attribute (Vertex Attribute)： Coordinates and color values
Primitives (Primitive)： The rendering type to be represented by the vertex attribute . Such as GL_POINTS、GL_TRIANGLES、GL_LINE_STRIP etc.
Fragment Shader ： The main purpose is to calculate the final color of a pixel

Vertex buffer object (VBO)： Send a large number of vertex data to video memory at one time （ Memory of graphics card ）, For vertex shaders .VBO The buffer type of is ：GL_ARRAY_BUFFER

Vertex shader type ：GL_VERTEX_SHADER
Clip shader type ：GL_FRAGMENT_SHADER
Fragment Shader ： Calculate the final color output of pixels

• （ The vertices 、 fragment ） Shader usage steps ：

    1.  Use   Shader Language GLSL(OpenGL Shading Language) Write shaders 
    2.  Compiling shaders 
    3.  Using shaders 
  

Shader program ： Link multiple shaders , Link the output of each shader to the input of the next shader . When the output and input don't match , You will get a link error .

Link vertex properties ：

glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
glEnableVertexAttribArray(0); //  Turn on vertex properties , 0:  Vertex attribute position value 
0 ——  Vertex attributes to configure , Vertex shader program location value 
3 ——  The size of the vertex attribute 
GL_FLOAT —— location The data type of the variable to which the value refers 
GL_FALSE ——  Whether you want the data to be standardized , Don't want to 
3 * sizeof(float) ——  step (Stride)
(void*)0 ——  Location (location) The offset of the starting position of the data in the buffer 

Vertex array object (Vertex Array Object, VAO) Can be bound like a vertex buffer object , Any subsequent vertex attribute calls are stored in this VAO in . The good thing is , When configuring vertex attribute pointers , You only need to execute those calls once , When drawing objects later, you only need to bind the corresponding VAO That's it . This makes it easy to switch between different vertex data and attribute configurations , Just bind different VAO That's it . All the States just set will be stored in VAO in .

 Vertex data   >  （ Vertex array object VAO Mark 1） Vertex buffer object （VBO）>   Set vertex property pointer   >  Vertex shader   >  Fragment Shader  >  Shader program  +  Tag before binding 1 Vertex array object VAO >  The screen 

// ..::  Initialization code （ Only run once  ( Unless your objects change frequently )） :: ..
// 1.  binding VAO
glBindVertexArray(VAO);
// 2.  Copy the vertex array to the buffer for OpenGL Use 
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
// 3.  Set vertex property pointer 
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
glEnableVertexAttribArray(0);

[...]

// ..::  Draw code （ In the rendering loop ） :: ..
// 4.  Draw objects 
glUseProgram(shaderProgram); //  Using shader programs 
glBindVertexArray(VAO); //  Bind again when using VAO object ,VAO There are... In the object VBO All vertex attributes .
someOpenGLFunctionThatDrawsOurTriangle(); 
//  Such as drawing triangles : 
// glDrawArrays(GL_TRIANGLES, 0, 3); 
//  Parameter meaning ：OpenGL The type of element ,  The starting index of the vertex array ,  The number of vertices involved in painting 

Index buffer object
Index buffer object (Element Buffer Object,EBO, Also called Index Buffer Object,IBO)
Vertex array object VAO, You can save vertex buffer objects VBO Properties of , You can also save index buffer objects IBO The binding state of