[英]I can't get my OpenGL program to render a triangle
因此,我已经在OpenGL中编写了一个模型加载器,并且实际上加载了模型,但是由于某种原因,我无法在屏幕上看到生成的三角形。 看一下自己:
#define GLEW_STATIC
#include <GL\glew.h> // Graphics Libraries
#include <GLFW\glfw3.h>
#include <iostream>
#include <fstream>
#include <vector>
#include <string>
int main()
{
std::cout << "Please enter the name of the mesh file: ";
std::string FileName;
std::cin >> FileName;
std::cout << "You entered: " << FileName << std::endl;
if (!glfwInit())
{
std::cout << "Failed to initialize GLFW" << std::endl;
system("Pause");
return EXIT_FAILURE;
}
std::cout << "GLFW 3.0.4 Initialized" << std::endl;
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
GLFWwindow* Window = glfwCreateWindow(800, 600, "Window", NULL, NULL);
glfwMakeContextCurrent(Window);
if (Window == NULL)
{
std::cout << "Failed to create an OpenGL 3.3 context" << std::endl;
system("Pause");
return EXIT_FAILURE;
}
std::cout << "Created an OpenGL 3.3 context" << std::endl;
glewExperimental = GL_TRUE;
if (glewInit() != GLEW_OK)
{
std::cout << "Failed to initialize GLEW 1.11.0" << std::endl;
system("Pause");
return EXIT_FAILURE;
}
std::ifstream FileStream(FileName);
std::vector <float> Vertices;
if (!FileStream)
{
std::cout << "An error was encountered while opening "<< FileName << std::endl;
system("Pause");
return EXIT_FAILURE;
}
float coordinateX, coordinateY, coordinateZ;
std::string Character;
while (!FileStream.eof())
{
FileStream >> Character;
if (Character == "v")
{
FileStream >> coordinateX >> coordinateY >> coordinateZ;
std::cout << "Loading in " << coordinateX << " " << coordinateY << " " << coordinateZ << std::endl;
Vertices.push_back(coordinateX);
Vertices.push_back(coordinateY);
Vertices.push_back(coordinateZ);
}
else
{
std::cout << "Skipping " << Character << std::endl;
continue;
}
}
std::cout << "Loaded " << FileName << std::endl;
glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_LESS);
unsigned int VBO;
glGenBuffers(1, &VBO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(float) * Vertices.size(), &Vertices.front(), GL_STATIC_DRAW);
unsigned int VAO;
glGenVertexArrays(1, &VAO);
glBindVertexArray(VAO);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
const char* Vertex_Shader =
"#version 330\n"
"in vec3 vp;"
"void main () {"
" gl_Position = vec4 (vp, 1.0);"
"}";
const char* Fragment_Shader =
"#version 330\n"
"out vec4 frag_colour;"
"void main () {"
" frag_colour = vec4 (0.5, 0.0, 0.5, 1.0);"
"}";
unsigned int VertexShader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(VertexShader, 1, &Vertex_Shader, NULL);
glCompileShader(VertexShader);
unsigned int FragmentShader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(FragmentShader, 1, &Fragment_Shader, NULL);
glCompileShader(FragmentShader);
unsigned int Shader_Program = glCreateProgram();
glAttachShader(Shader_Program, FragmentShader);
glAttachShader(Shader_Program, VertexShader);
glLinkProgram(Shader_Program);
while (!glfwWindowShouldClose(Window))
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glUseProgram(Shader_Program);
glBindVertexArray(VAO);
glDrawArrays(GL_TRIANGLES, 0, Vertices.size());
glfwPollEvents();
glfwSwapBuffers(Window);
}
return EXIT_SUCCESS;
}
并加载的文件如下:
v 0.0 0.5 0.0
v 0.5 -0.5 0.0
v -0.5 -0.5 0.0
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
const char* Vertex_Shader =
"#version 330\n"
"in vec3 vp;"
"void main () {"
" gl_Position = vec4 (vp, 1.0);"
"}";
不能保证按声明顺序为属性分配属性槽。
您需要(通过location
限定符或glBindAttribLocation()
pre-link )告诉OpenGL将其放置在哪里,或询问( glGetAttribLocation()
后链接 )将其放置在哪里。
此代码中至少有3个问题:
它创建两个顶点着色器对象,没有片段着色器对象。 更换:
unsigned int FragmentShader = glCreateShader(GL_VERTEX_SHADER);
通过:
unsigned int FragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
glDrawArrays()
的第三个参数必须是顶点数,而此代码传入的是坐标总数。 由于此处使用每个顶点3个坐标,因此将调用更改为:
glDrawArrays(GL_TRIANGLES, 0, Vertices.size() / 3);
未指定顶点属性的位置。 这可以通过“意外”来解决,特别是只要只有一个属性。 但是指定位置要安全得多。 最简单的方法是将位置添加到顶点着色器的vp
声明中:
"layout(location = 0) in vec3 vp;"
GL_ARRAY_BUFFER
错误 1) 在 glBindVertexArray
调用之后,只需绑定(并创建)您的GL_ARRAY_BUFFER
。
2)如另一个答案中所述,您的片段着色器创建错误,应显示为: unsigned int FragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
3)您理所当然地会在着色器中获得正确的属性,这是不正确的做法。 你应该是明确的,并有一个类似的布局 : layout(location = X) in vec3 myVec;
也有几点提示:
无需在循环内重新绑定您的VAO,只需在while(!glfwWindowShouldClose(Window))
之前将其绑定。 您的着色器程序也是如此。
您应该检查着色器是否正确编译以及程序是否正确链接! 看看glGetShaderiv
, glGetProgramiv
与GL_COMPILE_STATUS
和GL_LINK_STATUS
分别; 以及glGetShaderInfoLog
和glGetProgramInfoLog
如果两种状态均未获得GL_TRUE
。
这将为您提供一条消息,告诉您在编译/链接时遇到的确切问题,因此您可以轻松地调试着色器代码而不必猜测。
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