无法在OpenGL中绘制三角形

时间:2016-06-23 22:39:29

标签: c opengl

我最近开始学习OpenGL并编写了一些代码来在SDL窗口中绘制一个简单的白色三角形。我已经阅读并重新阅读了我的代码,并且已经根据几个opengl教程中提出的内容进行了检查,但我无法使其工作。我知道opengl正确绑定到SDL,因为我可以使用glClearColor更改窗口背景颜色,但我无法显示该darn三角形。

我很乐意提供更多信息,但说实话,我不知道问题的确切来源,所以这里是我写的代码:

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

    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 1);

    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);

    gWindow = SDL_CreateWindow("Test OpenGL", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, WINWIDTH, WINHEIGHT, SDL_WINDOW_SHOWN | SDL_WINDOW_OPENGL);
    if (gWindow == NULL)
    {
        fprintf(stderr, "Failed to create window. SDL error : %s\n", SDL_GetError());
        SDL_Quit();
        return -1;
    }

    gGLContext = SDL_GL_CreateContext(gWindow);
    if (gGLContext == 0)
    {
        fprintf(stderr, "Failed to create OpenGL context. SDL error : %s\n", SDL_GetError());
        SDL_DestroyWindow(gWindow);
        SDL_Quit();
        return -1;
    }

    GLenum glewInitResult = glewInit();
    if (glewInitResult != GLEW_OK)
    {
        fprintf(stderr, "Failed to initialize glew. Glew error : %s\n", glewGetErrorString(glewInitResult));
        SDL_GL_DeleteContext(gGLContext);
        SDL_DestroyWindow(gWindow);
        SDL_Quit();
        return -1;
    }
    glEnable(GL_DEPTH_TEST);

    return 0;
}

int loadShader(char *filename, GLint *shader)
{
    long sz;
    const GLchar *code;
    FILE *fp = fopen(filename, "rb");
    if( !fp ) perror(filename),exit(1);

    fseek( fp , 0L , SEEK_END);
    sz = ftell( fp );
    rewind( fp );

    code = calloc( 1, sz+1 );
    if( !code ) fclose(fp),fputs("memory alloc fails",stderr),exit(1);

    if( 1!=fread( code , sz, 1 , fp) )
      fclose(fp),free(code),fputs("entire read fails",stderr),exit(1);

    fclose(fp);
    char *dot = strrchr(filename, '.');
    GLenum type;
    if (dot)
        type = !strcmp(dot, ".vs") ? GL_VERTEX_SHADER : GL_FRAGMENT_SHADER;
    *shader = glCreateShader(type);
    glShaderSource(*shader, 1, &code, NULL);
    glCompileShader(*shader);
    GLint status;
    glGetShaderiv(*shader, GL_COMPILE_STATUS, &status);

    char buffer[512];
    glGetShaderInfoLog(*shader, sizeof(buffer), NULL, buffer);
    fprintf(stderr, buffer);
    if (status != GL_TRUE)
        return -1;
    return 0;
}

void printError(char *message)
{
#define TEST(ERR) case ERR: fprintf(stderr, "%s : " #ERR "\n", message); break;
    int error;
    if ((error = glGetError()))
        switch (error)
        {
        TEST(GL_INVALID_ENUM)
        TEST(GL_INVALID_VALUE)
        TEST(GL_INVALID_OPERATION)
        TEST(GL_STACK_OVERFLOW)
        TEST(GL_STACK_UNDERFLOW)
        TEST(GL_OUT_OF_MEMORY)
        TEST(GL_INVALID_FRAMEBUFFER_OPERATION)
        TEST(GL_TABLE_TOO_LARGE)
    default:
        fprintf(stderr, "Unknown error\n");
        }
#undef TEST
}

int main(int argc, char *argv[])
{
    if (init() != 0)
        return -1;

    float vertices[] = {0.0,  0.5,
                        0.5, -0.5,
                        -.5, -0.5};
    GLuint vbo;
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    GLuint vShader;
    GLuint fShader;
    if (loadShader("plain_2d.vs", &vShader) < 0)
        return -1;
    if (loadShader("plain_2d.fs", &fShader) < 0)
        return -1;
    GLint shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vShader);
    glAttachShader(shaderProgram, fShader);
    glLinkProgram(shaderProgram);
    glUseProgram(shaderProgram);

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

    printError("Before entering the loop");

    SDL_Event e;
    int quit = 0;
    while (!quit)
    {
        printError("In the loop");
        while (SDL_PollEvent(&e))
        {
            switch (e.type)
            {
            case SDL_QUIT:
                quit = 1;
            }
        }

        glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        glDrawArrays(GL_TRIANGLES, 0, 3);

        SDL_GL_SwapWindow(gWindow);
    }
    return 0;
}

printError和loadShader是我写的辅助函数,我确信它们完美无缺。这是顶点和片段着色器的代码,这是基本的,我没有看到有什么错误来自那里:

VERTEX SHADER

#version 150

in vec2 position;

void main()
{
    gl_Position = vec4(position, 0.0, 1.0);
}

FRAGMENT SHADER

#version 150

out vec4 outColor;

void main()
{
    outColor = vec4(1.0, 1.0, 1.0, 1.0);
}

我很抱歉这是模糊的,但是我做了我的研究,并且在我的代码中找不到任何错误,所以我希望更有经验的人能够找到问题。

提前致谢!

3 个答案:

答案 0 :(得分:5)

您尚未生成和绑定顶点数组对象,只是顶点缓冲区。基本上你已经创建了一个数据源(VBO),但数据无处可去,所以当你调用glEnableVertexAttribArray(posAttrib);

时没有绑定数组对象

在生成并绑定缓冲区之前添加以下内容:

GLuint vao;
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);

编辑:启用兼容性配置文件时,3.1和更新的 中有默认的VAO - 核心配置文件要求您手动执行。

另外,请显示loadShader()

的来源

答案 1 :(得分:1)

通常,在创建着色器时,必须指定着色器类型:

GLuint vertexShader, fragmentShader;

vertexShader = glCreateShader(GL_VERTEX_SHADER);
fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);

我的代码中没有看到任何内容。 loadShader是否根据扩展名进行此检测?如果没有,这将是最可能的问题。

答案 2 :(得分:1)

我对你的代码进行了一些检查。一些错误的事情:

  • 您没有申请核心资料
  • 您不检查您的链接
  • 您正在滥用逗号运算符
  • 您没有启用glewExperimental
  • 你没有清除你的深度位

以下是使用上下文的差异(来自修改后的版本,因为您没有包含标题或定义):

@@ -22,6 +22,7 @@

     SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
     SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 1);
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);

     SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
     SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
@@ -43,6 +44,7 @@
         return -1;
     }

+    glewExperimental = GL_TRUE;
     GLenum glewInitResult = glewInit();
     if (glewInitResult != GLEW_OK)
     {
@@ -69,10 +71,10 @@
     rewind( fp );

     code = calloc( 1, sz+1 );
-    if( !code ) fclose(fp),fputs("memory alloc fails",stderr),exit(1);
+    if( !code ) {fclose(fp);fputs("memory alloc fails",stderr);exit(1);}

     if( 1!=fread( code , sz, 1 , fp) )
-      fclose(fp),free(code),fputs("entire read fails",stderr),exit(1);
+        {fclose(fp);free(code);fputs("entire read fails",stderr);exit(1);}

     fclose(fp);
     char *dot = strrchr(filename, '.');
@@ -122,6 +124,10 @@
     float vertices[] = {0.0,  0.5,
                         0.5, -0.5,
                         -.5, -0.5};
+    GLuint vao;
+    glGenVertexArrays(1, &vao);
+    glBindVertexArray(vao);
+
     GLuint vbo;
     glGenBuffers(1, &vbo);
     glBindBuffer(GL_ARRAY_BUFFER, vbo);
@@ -160,7 +166,7 @@
         }

         glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
-        glClear(GL_COLOR_BUFFER_BIT);
+        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

         glDrawArrays(GL_TRIANGLES, 0, 3);

结果:triangle