OpenGL渲染管道,Shader,VAO&VBO&EBO
OpenGL渲染管線
(也就是)OpenGL渲染一幀圖形的流程
- 以下列舉最簡單的,渲染一個三角形的流程,你可以將它視為 精簡版OpenGL渲染管線
更複雜的流程也僅僅就是:在此基礎上的各個流程中 添加額外的內容,而這些會在後續補充。
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- CPU將三角形的 [點坐標,及其索引資訊] 傳入GPU顯示記憶體
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- CPU調用 gl函數編譯鏈接掛載 shader
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- shader是使用 類C語言: glsl 編寫的程式
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- GPU會執行shader中的內容,並根據shader程式進行繪圖。
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- GPU會 匯總shader提供的數據&CPU提供的數據,並根據他們進行繪圖。
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- CPU調用 gl函數激活 GPU執行shader並繪製圖
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- 以下是相關程式碼:
// build and compile our shader program
// ------------------------------------
// vertex shader
unsigned int vertexShader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
glCompileShader(vertexShader);
// check for shader compile errors
int success;
char infoLog[512];
glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
if (!success)
{
glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
}
// fragment shader
unsigned int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
glCompileShader(fragmentShader);
// check for shader compile errors
glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
if (!success)
{
glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
}
// link shaders
unsigned int shaderProgram = glCreateProgram();
glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);
glLinkProgram(shaderProgram);
// check for linking errors
glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
if (!success) {
glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;
}
glDeleteShader(vertexShader);
glDeleteShader(fragmentShader);
// -----------------------------以上:Shader編譯,編譯檢查,鏈接,鏈接檢查-----------------------------
// set up vertex data (and buffer(s)) and configure vertex attributes
// ------------------------------------------------------------------
//三角形頂點,及其索引資訊:
float vertices[] = {
0.5f, 0.5f, 0.0f, // top right
0.5f, -0.5f, 0.0f, // bottom right
-0.5f, -0.5f, 0.0f, // bottom left
-0.5f, 0.5f, 0.0f // top left
};
unsigned int indices[] = { // note that we start from 0!
0, 1, 3, // first Triangle
1, 2, 3 // second Triangle
};
//向GPU傳入相關數據
unsigned int VBO, VAO, EBO;
glGenVertexArrays(1, &VAO);
glGenBuffers(1, &VBO);
glGenBuffers(1, &EBO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
glBindVertexArray(VAOID)
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
glEnableVertexAttribArray(0);
// note that this is allowed, the call to glVertexAttribPointer registered VBO as the vertex attribute's bound vertex buffer object so afterwards we can safely unbind
glBindBuffer(GL_ARRAY_BUFFER, 0);
// remember: do NOT unbind the EBO while a VAO is active as the bound element buffer object IS stored in the VAO; keep the EBO bound.
//glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
// You can unbind the VAO afterwards so other VAO calls won't accidentally modify this VAO, but this rarely happens. Modifying other
// VAOs requires a call to glBindVertexArray anyways so we generally don't unbind VAOs (nor VBOs) when it's not directly necessary.
glBindVertexArray(0);
while (!glfwWindowShouldClose(window)) {
// input
// -----
processInput(window);
// render
// ------
glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
// draw our first triangle
glUseProgram(shaderProgram);
glBindVertexArray(VAO);
// seeing as we only have a single VAO there's no need to bind it every time, but we'll do so to keep things a bit more organized
glDrawArrays(GL_TRIANGLES, 0, 6);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
// glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
// -------------------------------------------------------------------------------
glfwSwapBuffers(window);
glfwPollEvents();
}
// optional: de-allocate all resources once they've outlived their purpose:
// ------------------------------------------------------------------------
glDeleteVertexArrays(1, &VAO);
glDeleteBuffers(1, &VBO);
glDeleteBuffers(1, &EBO);
glDeleteProgram(shaderProgram);
VAO&VBO&EBO
1. VBO:一個抽象對象,OpenGL沒有固定它的實現,
因此你不必了解它的實現,你只需知道VBO是 OpenGL用來管理 來自CPU數據的 一種工具:
unsigned int VBOID, VAOID, EBOID; //申請三個整形值,用以存放 申請的VBO,VAB,EBO的 ID glGenBuffers(1, &VBOID); glGenVertexArrays(1, &VAOID); glGenBuffers(1, &EBOID); //向OpenGL申請: 1*VBO, 1*VAO, 1*EBO 並將其ID傳入各自的 地址
//[此地址可以是連續數組空間的首地址,也可以是單一的一個數據] glBindVertexArray(VAOID)
//將 glBindBuffer(GL_ARRAY_BUFFER, VBOID); //將VBOID指向的VBO 與flag:GL_ARRAY_BUFFER綁定。
2.