Question

我正在学习使用SDL2的OpenGL，并且跟随this tutorial，我已经来到绘制多边形 - ＆gt;着色器部分。但是，尽管我已经完成了教程指示的所有内容，但我无法从代码中获得任何输出，

#include <stdio.h>
#include <stdlib.h>
#include <string>
#include <iostream>

//Glew
#define GLEW_STATIC
#include <GL/glew.h>

//SDL headers
#include "SDL.h"
#include "SDL_opengl.h"

//OpenGL headers
#include <OpenGL/gl.h>
#include <OpenGL/glext.h>

//Constants
#define SCREEN_H 800
#define SCREEN_W 600
#define SCREEN_POS_X 0
#define SCREEN_POS_Y 0
#define SCREEN_FLAGS SDL_WINDOW_SHOWN|SDL_WINDOW_INPUT_FOCUS|SDL_WINDOW_MOUSE_FOCUS|SDL_WINDOW_OPENGL
//SDL_WINDOWPOS_CENTERED
bool done = false;

SDL_Window * pWindow = NULL;
SDL_GLContext pGLContext = NULL;

//Methods
int Init(void );
void GameLoop();
void Render();
void EventTick();
void Quit(void );

    // Shader sources
const GLchar* vertexSource = R"glsl(
    #version 150 core
    in vec2 position;
    void main()
    {
        gl_Position = vec4(position, 0.0, 1.0);
    }
)glsl";

const GLchar* fragmentSource = R"glsl(
    #version 150 core
    out vec4 outColor;
    void main()
    {
        outColor = vec4(1.0, 1.0, 1.0, 1.0);
    }
)glsl";


int main(int argc, char const *argv[])
{
    Init();
    GameLoop();
    Quit();
    return 0;
}

int Init()
{
    if(SDL_Init(SDL_INIT_VIDEO) < 0)
    {
        fprintf(stderr, "SDL_Error: %s\n", SDL_GetError());
        return -1;
    }

    //Compatibility
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 2);
    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
    SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);

    pWindow = SDL_CreateWindow("Main", SCREEN_POS_X, SCREEN_POS_Y, SCREEN_W, SCREEN_H, SCREEN_FLAGS);
    if (pWindow == NULL)
    {
        fprintf(stderr, "SDL_Error: %s\n", SDL_GetError());
        return -1;
    }

    pGLContext = SDL_GL_CreateContext(pWindow);

    glewExperimental = GL_TRUE;
    glewInit();


    return 0;
}

void GameLoop()
{
    printf("%s\n", glGetString(GL_SHADING_LANGUAGE_VERSION));
    printf("%s\n", glGetString(GL_VERSION));
    GLuint vao;
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);

    float Vertices[] = {
        0.0f, 20.0f,
        20.0f, 0.0f,
        20.0f, 20.0f
    };

    GLuint vbo;
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(Vertices), Vertices, GL_STATIC_DRAW);

    GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexSource, NULL);
    glCompileShader(vertexShader);

    //Check the vertex shader compilation
    GLint status_vertex;
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &status_vertex);
    if (status_vertex != GL_TRUE)
    {
        char buffer[512];
        glGetShaderInfoLog(vertexShader, 512, NULL, buffer);
        fprintf(stdout, "Vertex Shader: %s\n", buffer);
    }

    GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentSource, NULL);
    glCompileShader(fragmentShader);

    //Check the fragment shader compilation
    GLint status_fragment;
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &status_fragment);
    if (status_fragment != GL_TRUE)
    {
        char buffer[512];
        glGetShaderInfoLog(fragmentShader, 512, NULL, buffer);
        fprintf(stdout, "Fragment Shader: %s\n", buffer);
    }

    GLuint shaderProgram = glCreateProgram();
    if (shaderProgram == 0)
    {
        fprintf(stderr, "glGetError: %u\n", glGetError());
    }
    glBindAttribLocation(shaderProgram, 0, "position");
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glBindFragDataLocation(shaderProgram, 0, "outColor");
    glLinkProgram(shaderProgram);
    glUseProgram(shaderProgram);

    GLint posAttrib = glGetAttribLocation(shaderProgram, "position");
    glVertexAttribPointer(posAttrib, 2, GL_FLOAT, GL_FALSE, 0, 0);
    glEnableVertexAttribArray(posAttrib);

    GLint program_linked;
    glGetProgramiv(shaderProgram, GL_LINK_STATUS, &program_linked);
    if (program_linked != GL_TRUE)
    {
        GLsizei log_length = 0;
        GLchar message[1024];
        glGetProgramInfoLog(shaderProgram, 1024, &log_length, message);
        fprintf(stdout, "%s\n", message);
    }
    fprintf(stderr, "glGetError (End): %u\n", glGetError());
    fprintf(stderr, "SDL Error: %s\n", SDL_GetError());
    while(!done)
    {
        EventTick();
        Render();
    }
    fprintf(stderr, "glGetError (End): %u\n", glGetError());
    fprintf(stderr, "SDL Error: %s\n", SDL_GetError());

    glDeleteProgram(shaderProgram);
    glDeleteShader(fragmentShader);
    glDeleteShader(vertexShader);
    glDeleteBuffers(1, &vbo);
    glDeleteVertexArrays(1, &vao);
}

void Render()
{
    glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(0.0f, 1.0f, 0.0f);
    glDrawArrays(GL_TRIANGLES, 0, 3);
    SDL_GL_SwapWindow(pWindow);

}

void EventTick()
{
    SDL_Event s_GameEngEvent;
    while(SDL_PollEvent(&s_GameEngEvent))
    {
        switch(s_GameEngEvent.type)
        {
            case SDL_QUIT:
            {
                fprintf(stdout, "SQL is quitting...\n");
                done = true;
            }break;

            case SDL_KEYDOWN:
            {
                switch(s_GameEngEvent.key.keysym.scancode)
                {
                    case SDL_SCANCODE_ESCAPE:
                        {
                        fprintf(stdout, "SQL is quitting...\n");
                        done = true;
                        }break;
                    default:
                    break;
                }
            }break;
        }
    }

}

void Quit(void )
{
    //Destructions...
    SDL_GL_DeleteContext(pGLContext);
    SDL_DestroyWindow(pWindow);
    SDL_Quit();
}

我逐个使用代码的几个部分，并与原始code进行比较，但没有找到任何内容。

如果有人可以查看有问题的部分，我真的很感激。我的意思是我知道我没有尝试在上面编写好的代码，我试图关注OpenGL的工作原理，但目前我的目标是找到我正在制作的错误。

注意： 我不确定这些问题是否可以接受，如果是，请关闭它。

修改我使用g ++和c ++ 11编译代码。

Answer 1

您尝试绘制的三角形位于可见区域之外。默认情况下（这意味着没有应用任何投影/变换），可见区域在所有三个轴上从-1变为1。代码中使用的三角形与此区域不相交，因此不会渲染任何内容。

除此之外：您正在调用核心配置文件中不推荐使用的glColor3f函数。这应该报告您最可能没有看到的GL_INVALID_OPERATION，因为错误检查仅在renderloop结束时发生。你应该真正检查一下renderloop里面的错误。

即使OpenGL，SDL和GLSL都没有出现错误，也没有绘制多边形

1 个答案: