c - SDL 可调整大小的程序无法正确绘制 OpenGL

Question

上周我花了一美元买了一本旧的 OpenGL 书(OpenGL superbible designed for Windows 95)以为我可以获得一些在 3D 和 OpenGL 中绘图的想法。所有代码都使用这个奇怪的 Windows 库，所以我一直在将示例移植到 SDL OpenGL。我被困在一个可调整大小的窗口示例中，无论窗口大小如何，都会在中心绘制一个正方形。由于某种原因，该正方形仅在第一次调整大小时出现，之后无论我如何调整窗口大小时都不会再看到它。

有人知道问题出在哪里吗？

#include <stdio.h>
#include <stdlib.h>
#include "SDL.h"
#include "SDL_opengl.h"

#define TRUE 1
#define FALSE 0

#define WIN_WIDTH 500
#define WIN_HEIGHT 400
#define BPP 32

//go through and get the values to see if everything was set
int check_gl_init(int r_size, int g_size, int b_size, int dbuff) {
    int red, green, blue, doublebuf;

    SDL_GL_GetAttribute(SDL_GL_RED_SIZE, &red);
    if(red != r_size) { return FALSE; }
    SDL_GL_GetAttribute(SDL_GL_GREEN_SIZE, &green);
    if(green != g_size) { return FALSE; }
    SDL_GL_GetAttribute(SDL_GL_RED_SIZE, &blue);
    if(blue != b_size) { return FALSE; }
    SDL_GL_GetAttribute(SDL_GL_DOUBLEBUFFER, &doublebuf);
    if(dbuff != doublebuf) { return FALSE; }

    return TRUE;
}

int main(int argc, char** argv) {
    SDL_Init(SDL_INIT_EVERYTHING);
    atexit(SDL_Quit);

    SDL_Surface* screen;
    SDL_Event e;
    int w = WIN_WIDTH; int h = WIN_HEIGHT;
    Uint32 vid_flags = SDL_OPENGL | SDL_RESIZABLE;

    if(SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 8) < 0) { printf("opengl error: %s\n", SDL_GetError()); }
    if(SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 8) < 0) { printf("opengl error: %s\n", SDL_GetError()); }
    if(SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 8) < 0) { printf("opengl error: %s\n", SDL_GetError()); }
    if(SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8) < 0) { printf("opengl error: %s\n", SDL_GetError()); }
    if(SDL_GL_SetAttribute(SDL_GL_BUFFER_SIZE, 32) < 0) { printf("opengl error: %s\n", SDL_GetError()); }
    if(SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1) < 0) {
        printf("couldn't set double buffering: %s\n", SDL_GetError());
    } else { vid_flags |= SDL_DOUBLEBUF; }

    const SDL_VideoInfo* info = SDL_GetVideoInfo();
    if(info->hw_available == TRUE) { vid_flags |= SDL_HWSURFACE; } else { vid_flags |= SDL_SWSURFACE; }
    printf("hardware surfaces available?: %s\n", (info->hw_available == TRUE ? "yes" : "no"));
    if(info->blit_hw == TRUE) { vid_flags |= SDL_HWACCEL; }
    printf("hardware blits available?: %s\n", (info->blit_hw == TRUE ? "yes" : "no"));

    if(SDL_VideoModeOK(WIN_WIDTH, WIN_HEIGHT, BPP, vid_flags) == 0) {
        printf("error: video mode not supported: `%s'\n", SDL_GetError());
        return 0;
    }
    else {
        screen = SDL_SetVideoMode(WIN_WIDTH, WIN_HEIGHT, BPP, vid_flags);
        if(screen == NULL) {
            printf("no video: `%s'\n", SDL_GetError());
            return 0;
        }
    }

    if(check_gl_init(BPP / 4, BPP / 4, BPP / 4, TRUE) == FALSE) {
        printf("problem setting up opengl: %s\n", glGetString(glGetError()));
        return 0;
    }

    int running = TRUE;
    for(;running;) {
        //process events
        while(SDL_PollEvent(&e)) {
            if(e.type == SDL_VIDEORESIZE) {
                w = e.resize.w; h = e.resize.h;
                if(h == 0) { h = 1; } //prevent division by zero
                screen = SDL_SetVideoMode(w, h, BPP, vid_flags);
                if(screen == NULL) {
                    printf("sdl error, screen died: `%s'\n", SDL_GetError());
                }

                glViewport(0, 0, w, h); //x, y, w, h
                glLoadIdentity(); //reset coordinate system
                glMatrixMode(GL_PROJECTION);

                if(w <= h) {
                    glOrtho(0.0f, 250.0f, 0.0f, 250.0f * (h / w), 1.0, -1.0);
                }
                else {
                    glOrtho(0.0f, 250.0f * (w / h), 0.0f, 250.0f, 1.0, -1.0);
                }

                glMatrixMode(GL_MODELVIEW);
                glLoadIdentity();

                if(glGetError() != GL_NO_ERROR) {
                    printf("opengl error: %s\n", glGetString(glGetError()));
                }
            }
            if(e.type == SDL_QUIT) { running = FALSE; }
            if(e.type == SDL_KEYDOWN) { if(e.key.keysym.sym == SDLK_q) { running = FALSE; } }
        }

        glClearColor(0.0f, 0.0f, 1.0f, 1.0f); //clear with blue
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        glColor3f(1.0f, 0.0f, 0.0f); //red
        glRectf(100.0f, 150.0f, 150.0f, 100.0f);

        glFlush();
        SDL_GL_SwapBuffers();
        SDL_Delay(100);
    }

    SDL_Quit();
    return 0;
}

Answer 1

你有这个:

glLoadIdentity(); //reset coordinate system
glMatrixMode(GL_PROJECTION);

该序列会将单位矩阵加载到 GL_MODELVIEW 堆栈，因为这是在上次调整大小期间通过 glMatrixMode() 设置的最新堆栈。

glOrtho() 然后继续将新的正射投影矩阵乘以最后一个。如您所见，这不是很好。

设置矩阵模式，然后加载单位矩阵:

glMatrixMode(GL_PROJECTION);
glLoadIdentity(); //reset coordinate system