SDL2 C ++-多重圖像渲染錯誤

Question

在開始之前，我使用的IDE是Code :: Blocks。

我將在另一個與我的學習項目不同的項目中練習在線學習有關SDL的知識。 我想在背景頂部加載一個球的圖像。 在我的研究項目中效果很好。 我將代碼復制到測試項目中，然后球消失了。 僅背景可見。

我刪除了涉及背景的代碼，並且效果很好。

我的代碼：

#include <iostream>
#include <cstdlib>
#include <SDL.h>
#include <SDL_image.h>
#undef main

using namespace std;

SDL_Texture *LoadTexture (string filepath, SDL_Renderer *renderTarget){
    SDL_Texture *texture = 0;
    SDL_Surface *surface = IMG_Load(filepath.c_str());

    texture = SDL_CreateTextureFromSurface(renderTarget, surface);

    SDL_FreeSurface(surface);

    return texture;
}

int main () {

    SDL_Window *window = 0;
    SDL_Texture *ball = 0;
    SDL_Texture *background_sky = 0;

    SDL_Renderer *renderTarget = 0;

    int frameW, frameH;
    int textureW, textureH;

    //--Crop Instructions--//
    frameW = textureW / 1; //row division
    frameH = textureH / 1; //column division

    SDL_Rect ballcrop;
    ballcrop.x = ballcrop.y = 0;
    ballcrop.w = frameW; //length of selected area
    ballcrop.h = frameH; //height of selected area

    SDL_Rect ballpos;
    ballpos.x = ballpos.y = 10; //ball position
    ballpos.w = ballpos.h = 64; //size of crop
    //---------------------//

    SDL_Init(SDL_INIT_EVERYTHING);
    IMG_Init(IMG_INIT_PNG);

    window = SDL_CreateWindow("Ball", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 500, 500, SDL_WINDOW_SHOWN);
    renderTarget = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);

    ball = LoadTexture("ball.png", renderTarget);
    background_sky = LoadTexture("bg_sky.png", renderTarget);


    SDL_QueryTexture(ball, NULL, NULL, &textureW, &textureH); //crop action

    bool Active = true;
    SDL_Event ev;

    while (Active) {
        while (SDL_PollEvent(&ev)!=0) {
            if (ev.type == SDL_QUIT)
                Active = false;

            else if (ev.type == SDL_KEYDOWN) {
                switch (ev.key.keysym.sym) {
                case SDLK_UP:
                    ballpos.y -= 5;
                    break;
                case SDLK_DOWN:
                    ballpos.y += 5;
                    break;
                }
            }
        }
        SDL_RenderClear(renderTarget);

        SDL_RenderCopy(renderTarget, background_sky, NULL, NULL);
        SDL_RenderCopy(renderTarget, ball, &ballcrop, &ballpos);

        SDL_RenderPresent(renderTarget);
    }

    SDL_DestroyWindow(window);
    SDL_DestroyTexture(background_sky);
    SDL_DestroyTexture(ball);

    SDL_DestroyRenderer(renderTarget);

    window = 0;
    ball = background_sky = 0;
    renderTarget = 0;

    IMG_Quit();
    SDL_Quit();

    return 0;
}

我認為我不想顯示我的研究項目的源代碼，因為它的內容極其混亂。

任何幫助，將不勝感激 ：）

Answer 1

計算frameW和frameH ； 計算的代碼

//--Crop Instructions--//
frameW = textureW / 1; //row division
frameH = textureH / 1; //column division

在初始化之前使用textureW和textureH 。 移動整個“裁剪指令”塊，直到調用SDL_QueryTexture 。