使用OpenGL绘制点

Question

我的程序应该打开一个窗口，在中心画一个蓝色的点，但没能画出这个点。

这是我正在使用的完整代码：

#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <iostream>
#define numVAOs 1
GLuint renderingProgram;
GLuint vao[numVAOs];
GLuint createShaderProgram()
{
const char* vshaderSource = "#version 320 n"
"void main(void) n"
"{gl_Position = vec4(0.0,0.0,0.0,1.0);}";
const char* fshaderSource = "#version 320 n"
"out vec4 color; n"
"void main(void) n"
"{ color = vec4(0.0,0.0,1.0,1.0);}";
GLuint vShader = glCreateShader(GL_VERTEX_SHADER);
GLuint fShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(vShader, 1, &vshaderSource, NULL);
glShaderSource(fShader, 1, &fshaderSource, NULL);
glCompileShader(vShader);
glCompileShader(fShader);
GLuint vfProgram = glCreateProgram();
glAttachShader(vfProgram, vShader);
glAttachShader(vfProgram, fShader);
glLinkProgram(vfProgram);
return vfProgram;
}
void init(GLFWwindow* window) 
{
renderingProgram = createShaderProgram();
glGenVertexArrays(numVAOs, vao);
glBindVertexArray(vao[0]);
}
void display(GLFWwindow* window, double currentTime)
{

glUseProgram(renderingProgram);
glDrawArrays(GL_POINT, 0, 1);
}

int main(void)
{
if (!glfwInit())
{
return -1;
}
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 2);
GLFWwindow* window = glfwCreateWindow(600, 600, "Chapter2-program1", NULL, NULL);
glfwMakeContextCurrent(window);
//Window or OpenGL context creation failed
if (!window)
{
glfwTerminate();        
return -1;
}

if (glewInit() != GLEW_OK)                 
{
std::cout << "Error!" << std::endl;
exit(EXIT_FAILURE);
}
glfwSwapInterval(1);
init(window);   

/* Rendering loop- until the user closes the window */
while (!glfwWindowShouldClose(window))
{

/* Render here */
display(window, glfwGetTime());
/* Swap front and back buffers */
glfwSwapBuffers(window);
/* Poll for and process events */
glfwPollEvents();
}
glfwDestroyWindow(window);
glfwTerminate();   
exit(EXIT_SUCCESS);
return 0;
}

Answer 1

几个问题：

• #version 320不存在，它从OpenGL 3.2中的version 150变成了OpenGL 3.3中的version 330。

  下拉到#version 150，并确保检查着色器编译和链接日志。

• GL_POINT不是glDrawArrays()的mode参数的有效值，您想到的是GL_POINTS。

• 确保使用glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)清除颜色/深度缓冲区。

全部：

// g++ main.cpp `pkg-config glfw3 glew --cflags --libs`
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <iostream>
#define numVAOs 1
GLuint renderingProgram;
GLuint vao[numVAOs];
void CheckStatus( GLuint obj, bool isShader )
{
GLint status = GL_FALSE, log[ 1 << 11 ] = { 0 };
( isShader ? glGetShaderiv : glGetProgramiv )( obj, isShader ? GL_COMPILE_STATUS : GL_LINK_STATUS, &status );
if( status == GL_TRUE ) return;
( isShader ? glGetShaderInfoLog : glGetProgramInfoLog )( obj, sizeof( log ), NULL, (GLchar*)log );
std::cerr << (GLchar*)log << "n";
std::exit( EXIT_FAILURE );
}
void AttachShader( GLuint program, GLenum type, const char* src )
{
GLuint shader = glCreateShader( type );
glShaderSource( shader, 1, &src, NULL );
glCompileShader( shader );
CheckStatus( shader, true );
glAttachShader( program, shader );
glDeleteShader( shader );
}
const char* const vert = R"GLSL(
#version 150
void main(void)
{
gl_Position = vec4(0.0,0.0,0.0,1.0);
}
)GLSL";
const char* const frag = R"GLSL(
#version 150
out vec4 color;
void main(void)
{
color = vec4(0.0,0.0,1.0,1.0);
}    
)GLSL";
int main(void)
{
if (!glfwInit())
{
return -1;
}
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 2);
GLFWwindow* window = glfwCreateWindow(600, 600, "Chapter2-program1", NULL, NULL);
//Window or OpenGL context creation failed
if (!window)
{
glfwTerminate();        
return -1;
}
glfwMakeContextCurrent(window);
if (glewInit() != GLEW_OK)                 
{
std::cout << "Error!" << std::endl;
exit(EXIT_FAILURE);
}
glfwSwapInterval(1);
GLuint renderingProgram = glCreateProgram();
AttachShader( renderingProgram, GL_VERTEX_SHADER, vert );
AttachShader( renderingProgram, GL_FRAGMENT_SHADER, frag );
glLinkProgram( renderingProgram );
CheckStatus( renderingProgram, false );

glGenVertexArrays(numVAOs, vao);
glBindVertexArray(vao[0]);
/* Rendering loop- until the user closes the window */
while (!glfwWindowShouldClose(window))
{
/* Render here */
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );

glUseProgram(renderingProgram);
glDrawArrays(GL_POINTS, 0, 1);
/* Swap front and back buffers */
glfwSwapBuffers(window);
/* Poll for and process events */
glfwPollEvents();
}
glfwDestroyWindow(window);
glfwTerminate();   
exit(EXIT_SUCCESS);
return 0;
}