c++ - OpenGL - 一个简单的程序

Question

我正在学习 2D 图形，我正在尝试编写一个简单的程序来显示像 Sprite 一样的位图。我结合了几个代码来得到这个。应用程序运行正常(我的意思是它没有崩溃)，我们可以看到一个窗口，但没有显示图像。
这是代码:

#include <stdio.h>
#include <windows.h>
#include <GL/gl.h>
#include <GL/glext.h>
#include <GL/glu.h>

LRESULT CALLBACK WindowProcedure(HWND, UINT, WPARAM, LPARAM);
GLuint LoadBMP(const char *fileName);

char szClassName[ ] = "CodeBlocksWindowsApp";

int WINAPI WinMain(HINSTANCE hThisInstance, HINSTANCE hPrevInstance, LPSTR lpszArgument, int nCmdShow)
{
    HWND hwnd;
    MSG Msg;
    WNDCLASSEX wincl = {sizeof (WNDCLASSEX), CS_DBLCLKS, WindowProcedure, 0, 0, hThisInstance, LoadIcon (NULL, IDI_APPLICATION), LoadCursor (NULL, IDC_ARROW), (HBRUSH) COLOR_BACKGROUND, NULL, szClassName, LoadIcon (NULL, IDI_APPLICATION)};
    if (!RegisterClassEx(&wincl))
        return 0;
    hwnd = CreateWindowEx(0, szClassName, "Code::Blocks Template Windows App", WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT, 544, 375, HWND_DESKTOP, NULL, hThisInstance, NULL);
    ShowWindow (hwnd, nCmdShow);
            GLuint texture = LoadBMP("image.bmp");
            glEnable(GL_TEXTURE_2D);

            glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE,GL_REPLACE);
            glBindTexture(GL_TEXTURE_2D, texture);
            glBegin(GL_QUADS);
                glTexCoord2i(0, 0); glVertex2i(0, 0);
                glTexCoord2i(0, 1); glVertex2i(0, 64);
                glTexCoord2i(1, 1); glVertex2i(64, 64);
                glTexCoord2i(1, 0); glVertex2i(64, 0);
            glEnd();

            glDisable(GL_TEXTURE_2D);
    while (GetMessage (&Msg, NULL, 0, 0))
    {
        TranslateMessage(&Msg);
        DispatchMessage(&Msg);
    }
    return Msg.wParam;
}

LRESULT CALLBACK WindowProcedure(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)                  /* handle the Msg */
    {
        case WM_DESTROY:
            PostQuitMessage (0);       /* send a WM_QUIT to the message queue */
            break;
        default:                      /* for Msg that we don't deal with */
            return DefWindowProc (hwnd, message, wParam, lParam);
    }
    return 0;
}

GLuint LoadBMP(const char *fileName)
{
    FILE *file;
    unsigned char header[54];
    unsigned int dataPos;
    unsigned int size;
    unsigned int width, height;
    unsigned char *data;
    file = fopen(fileName, "rb");
    if (file == NULL)
    {
        MessageBox(NULL, "Error: Invaild file path!", "Error", MB_OK);
        return false;
    }
    if (fread(header, 1, 54, file) != 54)
    {
        MessageBox(NULL, "Error: Invaild file!", "Error", MB_OK);
        return false;
    }
    if (header[0] != 'B' || header[1] != 'M')
    {
        MessageBox(NULL, "Error: Invaild file!", "Error", MB_OK);
        return false;
    }
    dataPos     = *(int*)&(header[0x0A]);
    size        = *(int*)&(header[0x22]);
    width       = *(int*)&(header[0x12]);
    height      = *(int*)&(header[0x16]);
    if (size == NULL)
        size = width * height * 3;
    if (dataPos == NULL)
        dataPos = 54;

    data = new unsigned char[size];

    fread(data, 1, size, file);

    GLuint texture;
    glGenTextures(1, &texture);
    glBindTexture(GL_TEXTURE_2D, texture);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, data);
    return texture;
}

请告诉我，我做错了什么？

Answer 1

您确实创建了一个窗口，但没有创建 OpenGL context .没有 GL 上下文就不能使用 GL。在 Windows 上，创建 GL 上下文的 native API 是 wgl .这OpeGL.org wiki article解释了一些使用 wgl 的细节。

但是，您可能想要使用一些 GL 上下文和窗口管理库，它以独立于平台的方式抽象整个过程，这样只需几次调用，就可以创建一个支持 GL 的窗口。看看GLFW .这wiki article列出了更多此类库。