带有 OpenGL 4.4 的 SDL2：三角形未正确渲染
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【中文标题】带有 OpenGL 4.4 的 SDL2：三角形未正确渲染【英文标题】：SDL2 with OpenGL 4.4: Triangle Not Rendering Properly 【发布时间】：2015-08-08 05:57:41 【问题描述】：我正在使用带有 SDL2 的 OpenGL 4.4。我正在尝试使用顶点（-1、-1、0）、（1、-1、0）、（0、1、0）渲染一个简单的三角形。然而，当我认为我做的一切都正确时，什么都没有画出来。
我从我的项目中提取并重组了相关代码：
#include <cerrno>
#include <cstring>
#include <exception>
#include <fstream>
#include <iostream>
#include <string>
#include <GL/glew.h>
#include <GL/glu.h>
#include <SDL2/SDL.h>
#include <SDL2/SDL_opengl.h>
void init();
void cleanUp();
std::string loadShader(std::string filepath);
void checkShaderSuccess(GLuint shader);
SDL_Window* win;
SDL_GLContext glContext;
GLuint program, vertShader, fragShader, vao, vbo;
class GenError: public std::exception
public:
GenError():
exception(), msg("")
GenError(const std::string& m):
exception(), msg(m)
virtual ~GenError() throw()
virtual const char* what() const throw()
return msg.c_str();
private:
std::string msg;
;
int main()
init();
program = glCreateProgram();
if (program == 0)
throw GenError("Shader creation failed: "
"Could not find valid memory location in "
"constructor");
vertShader = glCreateShader(GL_VERTEX_SHADER);
fragShader = glCreateShader(GL_FRAGMENT_SHADER);
if (vertShader == 0 || fragShader == 0)
std::string m;
m += "Shader creation failed: "
"Could not find valid memory location when "
"adding shader: ";
m += (char *)gluErrorString(glGetError());
throw GenError(m);
std::cout << "Creating vertex shader..." << std::endl;
std::string data = loadShader("./shaders/basicVertex.vs");
const GLchar* data_c = data.c_str();
glShaderSource(vertShader, 1, &data_c, NULL);
glCompileShader(vertShader);
checkShaderSuccess(vertShader);
glAttachShader(program, vertShader);
std::cout << "Vertex shader created" << std::endl;
std::cout << "Creating fragment shader..." << std::endl;
data = loadShader("./shaders/basicFragment.fs");
data_c = data.c_str();
glShaderSource(fragShader, 1, &data_c, NULL);
glCompileShader(fragShader);
checkShaderSuccess(fragShader);
glAttachShader(program, fragShader);
std::cout << "Fragment shader created" << std::endl;
glLinkProgram(program);
GLint success;
glGetProgramiv(program, GL_LINK_STATUS, &success);
if (success == GL_FALSE)
GLint logLen = 0;
glGetProgramiv(program, GL_INFO_LOG_LENGTH, &logLen);
GLchar programLog[logLen];
glGetProgramInfoLog(program, logLen, &logLen, programLog);
std::string m;
m += "Failed to link program: ";
m += (char *)gluErrorString(glGetError());
m += ": ";
m += (char *)programLog;
throw GenError(m);
glValidateProgram(program);
glGetProgramiv(program, GL_VALIDATE_STATUS, &success);
if (success == GL_FALSE)
GLint logLen = 0;
glGetProgramiv(program, GL_INFO_LOG_LENGTH, &logLen);
GLchar programLog[logLen];
glGetProgramInfoLog(program, logLen, &logLen, programLog);
std::string m;
m += "Failed to validate program: ";
m += (char *)gluErrorString(glGetError());
m += ": ";
m += (char *)programLog;
throw GenError(m);
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
glGenBuffers(1, &vbo);
const GLfloat verts[] =
-1.0f, -1.0f, 0.0f,
1.0f, -1.0f, 0.0f,
0.0f, 1.0f, 0.0f
;
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glBufferData(GL_ARRAY_BUFFER,
sizeof(verts),
verts,
GL_STATIC_DRAW );
SDL_Event ev;
bool running = true;
while (true)
while (SDL_PollEvent(&ev))
if (ev.type == SDL_WINDOWEVENT &&
ev.window.event == SDL_WINDOWEVENT_CLOSE)
std::cout << "Closing window..." << std::endl;
running = false;
break;
if (!running) break;
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glUseProgram(program);
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glVertexAttribPointer(0,
3,
GL_FLOAT,
GL_FALSE,
3*sizeof(GLfloat),
(GLvoid*)0 );
glDrawArrays(GL_TRIANGLES, 0, 3);
glDisableVertexAttribArray(0);
SDL_GL_SwapWindow(win);
std::cout << "Window closed" << std::endl;
glDeleteBuffers(1, &vbo);
glDeleteVertexArrays(1, &vao);
glDeleteProgram(program);
glDeleteShader(vertShader);
glDeleteShader(fragShader);
cleanUp();
return 0;
void init()
std::cout << "Initializing..." << std::endl;
if (SDL_Init(SDL_INIT_VIDEO) != 0)
std::string m;
m.append("Error initializing SDL2: ");
m.append(SDL_GetError());
throw GenError(m);
SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 16);
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 4);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 4);
win = SDL_CreateWindow("Triangle Test",
SDL_WINDOWPOS_UNDEFINED,
SDL_WINDOWPOS_UNDEFINED,
800, 600,
SDL_WINDOW_OPENGL );
if (win == NULL)
throw GenError(SDL_GetError());
glContext = SDL_GL_CreateContext(win);
if (glContext == NULL)
std::string m;
m.append("Error associating window with OpenGL: SDL Error: ");
m.append(SDL_GetError());
throw GenError(m);
glewExperimental = GL_TRUE;
GLenum glewErr = glewInit();
if (glewErr != GLEW_OK)
std::string m;
m.append("Error initializing OpenGL GLEW extension: ");
m.append((const char*)glewGetErrorString(glewErr));
throw GenError(m);
else
/* GLEW does not play nice with OpenGL 4.4.
* GLEW thinks OpenGL 4.4 is "pretentious" and
* "entitled". GLEW likes to throw an invalid
* enumerant error the next time glGetError is
* called after GLEW's initialization.
* glGetError must be envoked to discard this
* faulty error. GLEW makes my code look sloppy.
* We do not like GLEW. We tolerate GLEW.
*/
GLenum junk = glGetError();
glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
glFrontFace(GL_CW);
glCullFace(GL_BACK);
glEnable(GL_CULL_FACE);
glEnable(GL_DEPTH_TEST);
glEnable(GL_FRAMEBUFFER_SRGB);
if(SDL_GL_SetSwapInterval(1) < 0)
std::cerr << "Warning: Unable to set VSync! "
<< "SDL Error: "
<< SDL_GetError() << std::endl;
GLenum error = glGetError();
if (error != GL_NO_ERROR)
std::string m;
m.append("Error initializing OpenGL: OpenGL Error: ");
m.append(reinterpret_cast<const char*>(gluErrorString(error)));
throw GenError(m);
std::cout << "Initialized" << std::endl;
void cleanUp()
std::cout << "Cleaning up..." << std::endl;
SDL_GL_DeleteContext(glContext);
SDL_DestroyWindow(win);
SDL_Quit();
std::cout << "Cleaned" << std::endl;
std::string loadShader(std::string filepath)
std::ifstream shaderFile(filepath.c_str());
if (!shaderFile.is_open())
std::cerr << "Could not load shader: "
<< "Error opening "
<< filepath
<< ": " << std::strerror(errno)
<< std::endl;
return std::string("");
std::string content, line;
while (std::getline(shaderFile, line))
content += line + '\n';
shaderFile.close();
return content;
void checkShaderSuccess(GLuint shader)
GLint success;
glGetShaderiv(shader, GL_COMPILE_STATUS, &success);
if (success == GL_FALSE)
GLint logLen = 0;
glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &logLen);
GLchar shaderLog[logLen];
glGetShaderInfoLog(shader, logLen, &logLen, shaderLog);
std::string m;
m += "Shader compilation failed: ";
m += (char *)gluErrorString(glGetError());
m += ": ";
m += (char *)shaderLog;
glDeleteShader(shader);
throw GenError(m);
...没有错误捕获（为了更快的浏览）：
#include <cerrno>
#include <cstring>
#include <exception>
#include <fstream>
#include <iostream>
#include <string>
#include <GL/glew.h>
#include <GL/glu.h>
#include <SDL2/SDL.h>
#include <SDL2/SDL_opengl.h>
void init();
void cleanUp();
std::string loadShader(std::string filepath);
SDL_Window* win;
SDL_GLContext glContext;
GLuint program, vertShader, fragShader, vao, vbo;
int main()
init();
program = glCreateProgram();
vertShader = glCreateShader(GL_VERTEX_SHADER);
fragShader = glCreateShader(GL_FRAGMENT_SHADER);
std::cout << "Creating vertex shader..." << std::endl;
std::string data = loadShader("./shaders/basicVertex.vs");
const GLchar* data_c = data.c_str();
glShaderSource(vertShader, 1, &data_c, NULL);
glCompileShader(vertShader);
glAttachShader(program, vertShader);
std::cout << "Vertex shader created" << std::endl;
std::cout << "Creating fragment shader..." << std::endl;
data = loadShader("./shaders/basicFragment.fs");
data_c = data.c_str();
glShaderSource(fragShader, 1, &data_c, NULL);
glCompileShader(fragShader);
glAttachShader(program, fragShader);
std::cout << "Fragment shader created" << std::endl;
glLinkProgram(program);
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
glGenBuffers(1, &vbo);
const GLfloat verts[] =
-1.0f, -1.0f, 0.0f,
1.0f, -1.0f, 0.0f,
0.0f, 1.0f, 0.0f
;
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glBufferData(GL_ARRAY_BUFFER,
sizeof(verts),
verts,
GL_STATIC_DRAW );
SDL_Event ev;
bool running = true;
while (true)
while (SDL_PollEvent(&ev))
if (ev.type == SDL_WINDOWEVENT &&
ev.window.event == SDL_WINDOWEVENT_CLOSE)
std::cout << "Closing window..." << std::endl;
running = false;
break;
if (!running) break;
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glUseProgram(program);
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glVertexAttribPointer(0,
3,
GL_FLOAT,
GL_FALSE,
3*sizeof(GLfloat),
(GLvoid*)0 );
glDrawArrays(GL_TRIANGLES, 0, 3);
glDisableVertexAttribArray(0);
SDL_GL_SwapWindow(win);
std::cout << "Window closed" << std::endl;
glDeleteBuffers(1, &vbo);
glDeleteVertexArrays(1, &vao);
glDeleteProgram(program);
glDeleteShader(vertShader);
glDeleteShader(fragShader);
cleanUp();
return 0;
void init()
std::cout << "Initializing..." << std::endl;
SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 16);
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 4);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 4);
win = SDL_CreateWindow("Triangle Test",
SDL_WINDOWPOS_UNDEFINED,
SDL_WINDOWPOS_UNDEFINED,
800, 600,
SDL_WINDOW_OPENGL );
glContext = SDL_GL_CreateContext(win);
glewExperimental = GL_TRUE;
GLenum glewErr = glewInit();
glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
glFrontFace(GL_CW);
glCullFace(GL_BACK);
glEnable(GL_CULL_FACE);
glEnable(GL_DEPTH_TEST);
glEnable(GL_FRAMEBUFFER_SRGB);
std::cout << "Initialized" << std::endl;
void cleanUp()
std::cout << "Cleaning up..." << std::endl;
SDL_GL_DeleteContext(glContext);
SDL_DestroyWindow(win);
SDL_Quit();
std::cout << "Cleaned" << std::endl;
std::string loadShader(std::string filepath)
std::ifstream shaderFile(filepath.c_str());
std::string content, line;
while (std::getline(shaderFile, line))
content += line + '\n';
shaderFile.close();
return content;
...我的顶点着色器（GLSL）：
#version 440
layout (location = 0) in vec3 position;
void main()
gl_Position = vec4(0.5 * position, 1.0);
...和我的片段着色器：
#version 440
out vec4 fragColor;
void main()
fragColor = vec4(0.0, 1.0, 1.0, 1.0);
现在很奇怪，当我从这里更改 C++ 代码中的第 148 行（带有错误捕获）时...
3*sizeof(GLfloat),
...到这个（换句话说，改变步幅）...
3*sizeof(GLdouble),
...编译和运行会生成一个三角形，其顶点为 (-1, -1, 0), (0, 0, 0), (0, 1, 0)。第二个顶点显然变得模糊了。我得到的是不等腰三角形，而不是等腰三角形。
我想 1) 弄清楚如何修复我的程序，使其显示具有指定顶点的三角形，以及 2) 了解我最初做错了什么，导致我在修改上述代码行时出现了如此奇怪的结果.
我已经对此进行了将近一周的修改。 任何见解表示赞赏。谢谢！
【问题讨论】：
您可以尝试不启用剔除吗？删除glEnable(GL_CULL_FACE) 调用。据我所知，您为三角形方向指定顺时针方向，但绘制一个逆时针三角形。所以它会被剔除。
@reto-koradi 成功了！注释掉 glEnable(GL_CULL_FACE) 使三角形可见。重新启用面相关多边形剔除后，我切换了三角形的第二个和第三个顶点以吸引逆时针剔除偏差（或任何技术术语）。所以 ((-1, -1, 0), (1, -1, 0), (0, 1, 0)) 变成了 ((-1, -1, 0), (0, 1, 0), ( 1, -1, 0))。这样做会导致我的三角形按需要渲染。非常感谢！如果没有人超过我，我稍后会尝试为我的问题添加官方答案。
糟糕。我的意思是顺时针不是逆时针。
【参考方案1】：
您的代码在多边形的缠绕顺序方面存在问题。您为正面指定顺时针缠绕，并启用背面的剔除：
glFrontFace(GL_CW);
glCullFace(GL_BACK);
但是三角形的缠绕顺序是逆时针的：
const GLfloat verts[] =
-1.0f, -1.0f, 0.0f,
1.0f, -1.0f, 0.0f,
0.0f, 1.0f, 0.0f
;
这意味着三角形将被剔除。
使用逆时针缠绕是 OpenGL 的主要标准，也是默认设置。所以最好的选择是您只需删除这行代码：
glFrontFace(GL_CW);
这将使GL_CCW 的值与您的几何形状相匹配。
禁用背面剔除始终是当多边形不显示时您应该做的第一件事。缠绕顺序错误是导致事物无法渲染的最常见原因之一，只需禁用剔除并检查是否会显示几何图形，就可以很容易地进行分类。
【讨论】：
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