[英]Setting attributes in the vertex shader in openGL
我最近一直在學習 OpenGL,我對着色器和 VBO 有點困惑。 基本上,我對頂點着色器如何知道 VBO 中的顏色和位置數據感到困惑。 據我所知glBindAttribLocation(program, attribute, variable);
是在着色器中設置屬性的原因,但是當我注釋掉該代碼時,三角形的顏色仍然可以很好地呈現。
這是我的代碼:
public static void main(String[] args) {
String vertexSource = "#version 400 core\n"
+ "in vec3 position;\n"
+ "in vec3 colour;\n"
+ "out vec3 vertexColour;\n"
+ "uniform mat4 model;\n"
+ "uniform mat4 view;\n"
+ "uniform mat4 projection;\n"
+ "void main() {\n"
+ "vertexColour = colour;\n"
+ "mat4 mvp = projection * view * model;\n"
+ "gl_Position = vec4(position, 1.0);\n"
+ "}\n";
String fragmentSource = "#version 400 core\n"
+ "in vec3 vertexColour;\n"
+ "out vec4 colours;\n"
+ "void main()\n"
+ "{\n"
+ " colours = vec4(vertexColour, 1);\n"
+ "}";
glfwSetErrorCallback(errorCallBack);
if (!glfwInit()) {
throw new IllegalStateException("Unable to initialize GLFW");
}
glfwDefaultWindowHints();
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GLFW_TRUE);
glfwWindowHint(GLFW_VISIBLE, GL_TRUE);
glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);
long window = glfwCreateWindow(640, 480, "my window!", 0, 0);
glfwSetKeyCallback(window, keyCallback);
if (window == 0) {
glfwTerminate();
throw new RuntimeException("Failed to create the GLFW window");
}
glfwMakeContextCurrent(window);
GL.createCapabilities();
float[] vertexPoints = {
0f,0.5f,0f,
-0.5f,-0.5f,0f,
0.5f,-0.5f,0f
};
float[] colours = {
0.1f,0.5f,0.5f,
0.3f,0.7f,0.9f,
0.4f,0.9f,0.1f
};
ArrayList<Integer> vaos = new ArrayList<Integer>();
ArrayList<Integer> vbos = new ArrayList<Integer>();
int vaoID = glGenVertexArrays();
vaos.add(vaoID);
glBindVertexArray(vaoID);
FloatBuffer vertices = BufferUtils.createFloatBuffer(vertexPoints.length);
vertices.put(vertexPoints);
vertices.flip();
int vboID = GL33.glGenBuffers();
vbos.add(vboID);
glBindBuffer(GL_ARRAY_BUFFER, vboID);
glBufferData(GL_ARRAY_BUFFER, vertices, GL_STATIC_DRAW);
//add it to the vao at position 0, size 3, with data types of float, normalised = false,
glVertexAttribPointer(0, 3, GL_FLOAT, false, 0, 0);
//unbind currently bound vbo
glBindBuffer(GL_ARRAY_BUFFER, 0);
//and one for the colour data
vboID = glGenBuffers();
glBindBuffer(GL_ARRAY_BUFFER, vboID);
glBufferData(GL_ARRAY_BUFFER, colours, GL_STATIC_DRAW);
glVertexAttribPointer(1, 3, GL_FLOAT, false, 0, 0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
//finished with vao now unbind it
glBindVertexArray(0);
//vao and vbo stuff is now finished with
//now for the shader stuff
int vertexShaderID = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertexShaderID, vertexSource);
glCompileShader(vertexShaderID);
if (!checkForSuccess(vertexShaderID)) {
glfwTerminate();
throw new IllegalStateException("vertex shader failed: " + glGetShaderInfoLog(vertexShaderID));
}
int fragmentShaderID = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragmentShaderID, fragmentSource);
glCompileShader(fragmentShaderID);
if (!checkForSuccess(vertexShaderID)) {
glGetShaderInfoLog(vertexShaderID);
glfwTerminate();
throw new IllegalStateException("fragment shader failed");
}
//shader program
int shaderProgramID = glCreateProgram();
glAttachShader(shaderProgramID, vertexShaderID);
glAttachShader(shaderProgramID, fragmentShaderID);
glLinkProgram(shaderProgramID);
//error test
int status = glGetProgrami(shaderProgramID, GL_LINK_STATUS);
if (status != GL_TRUE) {
glfwTerminate();
throw new RuntimeException(glGetProgramInfoLog(shaderProgramID));
}
glUseProgram(shaderProgramID);
//setting position attribute in the shader:
int positionAttribute = glGetAttribLocation(shaderProgramID, "position");
glEnableVertexAttribArray(positionAttribute);
glBindAttribLocation(shaderProgramID, positionAttribute, "position");
//setting colour attribute in the shader:
int colourAttribute = glGetAttribLocation(shaderProgramID, "colour");
glEnableVertexAttribArray(colourAttribute);
glBindAttribLocation(shaderProgramID, colourAttribute, "colour");
glClearColor(0.5f,0.5f,0.5f,1f);
//this will create a wire frame view
//glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
glfwShowWindow(window); //optional
while (!glfwWindowShouldClose(window)) {
double time = glfwGetTime();
glfwPollEvents();
glClear(GL_COLOR_BUFFER_BIT);
glBindVertexArray(vaoID);
//enables the position attribute in the vertex shader
glEnableVertexAttribArray(0);
//enables the colour attribute in the vertex shader
glEnableVertexAttribArray(1);
glDrawArrays(GL_TRIANGLES, 0, vertexPoints.length);
//disables the position and colour attribute in the vertex shader
glDisableVertexAttribArray(0);
glDisableVertexAttribArray(1);
glfwSwapBuffers(window);
}
//clear vaos and vbos
for (int vao : vaos) {
glDeleteVertexArrays(vao);
}
for (int vbo : vbos) {
glDeleteBuffers(vbo);
}
//delete shaders
glDetachShader(shaderProgramID, vertexShaderID);
glDetachShader(shaderProgramID, fragmentShaderID);
glDeleteShader(vertexShaderID);
glDeleteShader(fragmentShaderID);
glDeleteProgram(shaderProgramID);
Callbacks.glfwFreeCallbacks(window);
glfwDestroyWindow(window);
glfwTerminate();
}
我在 github 上提供了我的完整代碼文件(250 行): https : //github.com/OneEgg42/opengl
有人會這么好心並向我解釋這是如何工作的嗎?
提前致謝!
VBO 和着色器之間的關系不是由glBindAttribLocation
建立的。
相關線路實際上是
glBindBuffer(GL_ARRAY_BUFFER, vboID);
glVertexAttribPointer(0, 3, GL_FLOAT, false, 0, 0);
您告訴 OpenGL 位置為 0 的屬性(第一個glVertexAttribPointer
調用中的第一個參數)應該從vboID
讀取前三個浮點數。
glBindAttribLocation
負責將某個屬性綁定到特定位置。 由於這必須在鏈接着色器之前完成,因此它們不會在您的代碼中執行任何操作。 更重要的是,因為這段代碼告訴屬性使用它已經擁有的位置:
int positionAttribute = glGetAttribLocation(shaderProgramID, "position");
glEnableVertexAttribArray(positionAttribute);
glBindAttribLocation(shaderProgramID, positionAttribute, "position");
您基本上是查詢位置,然后再次將位置分配給屬性。
兩個邊注:
目前,您的代碼完全靠運氣。 你假設在glVertexAttribPointer(0, 3, GL_FLOAT, false, 0, 0);
“位置”屬性位於位置 0 的行,只要它是着色器中寫入的第一個屬性,它就可能是。 顏色也一樣。 當您在着色器中交換兩個屬性定義的順序時,您的代碼很可能會中斷。 使用glGetAttribLocation
查詢屬性位置並使用結果而不是 0 和 1,或者在鏈接之前使用glBindAttribLocation
以確保屬性位於您期望的位置。
對glEnableVertexAttribArray
的調用應該在 VAO 設置代碼中,而不是在渲染循環中。
設置:
glBindBuffer(GL_ARRAY_BUFFER, vboID);
glBufferData(GL_ARRAY_BUFFER, vertices, GL_STATIC_DRAW);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 3, GL_FLOAT, false, 0, 0);
使成為:
glBindVertexArray(vaoID);
glDrawArrays(GL_TRIANGLES, 0, vertexPoints.length);
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