我目前正在尝试学习如何在使用SDL2花费一些时间后在C ++中使用OpenGL，并且我正努力让我的三角形显示在屏幕上。我一直在学习一系列教程，并试图深入了解一切是如何运作的。我成功地将一个简单的纯色三角形显示在屏幕上，但是当我尝试给每个顶点一个不同的颜色时，除了背景之外没有任何颜色显示。
#include <iostream>
#include <string>
#include <GL/glew.h>
#include <GL/GLU.h>
#include <SDL.h>
#include <SDL_opengl.h>
//***************************************************************************
// The Width of the screen
//***************************************************************************
const GLuint SCREEN_WIDTH = 800;
//***************************************************************************
// The height of the screen
//***************************************************************************
const GLuint SCREEN_HEIGHT = 600;
bool success = GL_TRUE;
const GLchar* vertexShaderSource = "#version 330 core\n"
"layout (location = 0) in vec3 position;\n"
"layout (location = 1) in vec3 color;\n"
"out vec3 ourColor;\n"
"void main()\n"
"{\n"
"gl_Position = vec4(position, 1.0);\n"
"ourColor = color;\n"
"}\0";
const GLchar* fragmentShaderSource = "#version 330 core\n"
"in vec3 ourColor;\n"
"out vec4 color;\n"
"void main()\n"
"{\n"
"color = vec4(ourColor, 1.0f);\n"
"}\n\0";
bool quit;
int main(int argc, char *argv[])
{
//***********************************************************************
// Initialize SDL
//***********************************************************************
if (SDL_Init(SDL_INIT_EVERYTHING) < 0)
{
std::cout << "SDL could not initialize!SDL Error :" <<
std::string(SDL_GetError());
return EXIT_FAILURE;
}
else
{
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 3);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK,
SDL_GL_CONTEXT_PROFILE_CORE);
SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
//*******************************************************************
//The window we'll be rendering to
//*******************************************************************
SDL_Window *window = SDL_CreateWindow("Triangle",
SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, SCREEN_WIDTH,
SCREEN_HEIGHT, SDL_WINDOW_SHOWN |
SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE);
if (window == NULL)
{
std::cout << "Window could not be created!SDL_Error: " <<
std::string(SDL_GetError()) << std::endl;
return EXIT_FAILURE;
}
//*******************************************************************
//OpenGL context
//*******************************************************************
SDL_GLContext context = SDL_GL_CreateContext(window);
//*******************************************************************
// Set the required callback functions
//*******************************************************************
SDL_Event windowEvent;
//*******************************************************************
//Use OpenGL 3.3
//*******************************************************************
//*******************************************************************
// Set this to true so GLEW knows to use a modern approach to
// retrieving function pointers and extensions
//*******************************************************************
glewExperimental = GL_TRUE;
//*******************************************************************
// Initialize GLEW to setup the OpenGL Function pointers
//*******************************************************************
GLenum glewError = glewInit();
if (GLEW_OK != glewError)
{
std::cout << "Failed to initialize GLEW: " <<
glewGetErrorString(glewError) << std::endl;
return EXIT_FAILURE;
}
glEnable(GL_CULL_FACE);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
//*******************************************************************
// Build and compile our shader program
// Vertex shader
//*******************************************************************
GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
glCompileShader(vertexShader);
//*******************************************************************
// Check for compile time errors
//*******************************************************************
GLint success;
GLchar infoLog[512];
glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
if (!success)
{
glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED: " <<
infoLog << std::endl;
}
//*******************************************************************
// Fragment shader
//*******************************************************************
GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
glCompileShader(fragmentShader);
//*******************************************************************
// Check for compile time errors
//*******************************************************************
glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
if (!success)
{
glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED: " <<
infoLog << std::endl;
}
//*******************************************************************
// Link shaders
//*******************************************************************
GLuint 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: " << infoLog << std::endl;
}
glDeleteShader(vertexShader);
glDeleteShader(fragmentShader);
//*******************************************************************
// Set up vertex data (and buffer(s)) and attribute pointers
//*******************************************************************
GLfloat vertices[] = {
// Positions // Colors
0.5f, -0.5f, 0.0f, 1.0f, 0.0f, 0.0f, // Bottom Right
-0.5f, -0.5f, 0.0f, 0.0f, 1.0f, 0.0f, // Bottom Left
0.0f, 0.5f, 0.0f, 0.0f, 0.0f, 1.0f // Top
};
GLfloat colors[] = {
1.0f, 0.0f, 0.0f, 1.0f,
0.0f, 1.0f, 0.0f, 1.0f,
0.0f, 0.0f, 1.0f, 1.0f
};
GLuint VBO, VAO;
glGenVertexArrays(1, &VAO);
glGenBuffers(1, &VBO);
//*******************************************************************
// Bind the Vertex Array Object first, then bind and set vertex
// buffer(s) and attribute pointer(s).
//*******************************************************************
glBindVertexArray(VAO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
// Position attribute
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), (GLvoid *)0);
glEnableVertexAttribArray(0);
// Color attribute
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), (GLvoid *)(3 * sizeof(GLfloat)));
glEnableVertexAttribArray(1);
//*******************************************************************
// Note that this is allowed, the call to glVertexAttribPointer
// registered VBO as the currently bound vertex buffer object so
// afterwards we can safely unbind
//*******************************************************************
glBindBuffer(GL_ARRAY_BUFFER, 0);
//*******************************************************************
// Unbind VAO (it's always a good thing to unbind any buffer/array to
// prevent strange bugs)
//*******************************************************************
glBindVertexArray(0);
//*******************************************************************
// DeltaTime variables
//*******************************************************************
GLdouble deltaTime = 0.0f;
Uint64 lastFrame = 0L;
Uint64 currentFrame = SDL_GetPerformanceCounter();
quit = false;
while (!quit)
{
//***************************************************************
// Calculate delta time
//***************************************************************
lastFrame = currentFrame;
currentFrame = SDL_GetPerformanceCounter();
deltaTime = ((currentFrame - lastFrame) * 1000 /
(GLdouble)SDL_GetPerformanceFrequency());
double tmpDeltaTime = deltaTime;
//std::cout << "Hello 1 - deltaTime: " << std::to_string(deltaTime) <<
// std::endl;
if (SDL_PollEvent(&windowEvent))
{
if (windowEvent.type == SDL_QUIT)
{
quit = true;
}
}
//***************************************************************
// Clear the colorbuffer and render
//***************************************************************
glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
//***************************************************************
// Draw our first triangle
//***************************************************************
glUseProgram(shaderProgram);
glBindVertexArray(VAO);
glDrawArrays(GL_TRIANGLES, 0, 3);
glBindVertexArray(0);
//***************************************************************
// draw OpenGL: Swap the screen buffers
//***************************************************************
SDL_GL_SwapWindow(window);
}
//***************************************************************
// Properly de-allocate all resources once they've outlived their
// purpose
//***************************************************************
glDeleteVertexArrays(1, &VAO);
glDeleteBuffers(1, &VBO);
glDeleteProgram(shaderProgram);
SDL_GL_DeleteContext(context);
SDL_DestroyWindow(window);
SDL_Quit();
}
return EXIT_SUCCESS;
}
正如您所知，我试图在同一个项目中同时使用OpenGL和SDL2。当我运行此代码时控制台显示没有错误，我得到了我的绿色背景，但根本没有三角形。我已经重复了几个＆＃34;着色器如何工作＆＃34;视频，看我是否错过任何东西，但似乎无法找到我的问题的根源。我错过了什么？
答案 0 :(得分：3)
您的程序是有效的GL程序，不应生成任何错误。它正确地绘制背景颜色，并且正确地不绘制任何三角形。
GL中的默认正面方向是逆时针方向（GL_CCW）。您定义的三角形在剪辑空间中顺时针定向（以及所有后续空间NDC和窗口空间）。结果，
glEnable(GL_CULL_FACE);
将具有在光栅化之前剔除三角形的效果。要查看三角形，请禁用（只是不启用它，默认情况下它是关闭的）GL_CULL_FACE，或者通过glFrontFace(GL_CW)将正面约定设置为顺时针，或者只设置glCullFace(GL_FRONT)让GL剔除正面，或者只是交换数组中的任意两个顶点。