效果图如下

本文主要将我们通过创建窗口、渲染上下文工具、纹理工具、矩形框工具；其需要主要的是：首先我们在显示BMP时，需要先创建好窗口，再使用渲染工具对窗口进行格式刷，使用纹理工具和渲染工具配合进行BMP图片显示，矩形框的作用就是显示BMP图片的大小。

下面小例子就是当鼠标点击时，会通过texture纹理工具，使用渲染拷贝一份纹理显示至window窗口

#include "playthread.h"
#include <SDL2/SDL.h>
#include <QDebug>
#include <QFile>//#号自动添加双引号“”
#define END(judge,SDL_Init) \if(judge) \{\qDebug() << #SDL_Init << "error" << SDL_GetError();\goto end;\}playThread::playThread(QObject *parent) : QThread(parent)
{//监听线程，线程结束后自动释放线程内存connect(this,&playThread::finished,this,&playThread::deleteLater);
}playThread::~playThread()
{disconnect();//?requestInterruption();quit();wait();qDebug() << "析构了";
}void playThread::run()
{//创建窗口SDL_Window *window = nullptr;//渲染上下文SDL_Renderer *renderer = nullptr;//纹理(直接跟特定驱动程序相关的像素数据)SDL_Texture *texture = nullptr;//矩形框SDL_Rect dstRect = {0,0,50,50};//初始化子系统END(SDL_Init(SDL_INIT_VIDEO),SDL_Init);//创建一个窗口//标题-X-Y-width-heightwindow = SDL_CreateWindow("SDL修改渲染目标",SDL_WINDOWPOS_UNDEFINED,SDL_WINDOWPOS_UNDEFINED,500,500,SDL_WINDOW_SHOWN);END(!window,SDL_CreateWindow);//创建渲染上下文--用于渲染图形到窗口//这SDL_RENDERER_ACCELERATED -- 个标志告诉 SDL 尝试创建一个使用硬件加速的渲染器//SDL_RENDERER_PRESENTVSYNC -- 这个标志使渲染器的呈现操作同步到显示器的垂直同步（VSync）renderer = SDL_CreateRenderer(window, -1,SDL_RENDERER_ACCELERATED |SDL_RENDERER_PRESENTVSYNC);//如果创建失败if(!renderer){renderer = SDL_CreateRenderer(window,-1,0);END(!renderer,SDL_CreateRenderer);}//创建纹理texture = createTexture(renderer);END(!texture,SDL_CreateTextureFromSurface);//设置渲染目标为windows -- nullptr默认为windowsEND(SDL_SetRenderTarget(renderer,nullptr),SDL_SetRenderTarget);//设置绘制颜色（画笔颜色）END(SDL_SetRenderDrawColor(renderer,0,0,0,SDL_ALPHA_OPAQUE),SDL_SetRenderDrawColor);//用绘制颜色（画笔颜色）清除渲染目标---也就是覆盖END(SDL_RenderClear(renderer),SDL_RenderClear);//拷贝纹理到渲染目标END(SDL_RenderCopy(renderer,texture,nullptr,&dstRect),SDL_rSDL_RenderCopyen);//更新所有的渲染操作到屏幕上SDL_RenderPresent(renderer);//等待退出事件while(!isInterruptionRequested()){SDL_Event event;SDL_WaitEvent(&event);switch(event.type){case SDL_QUIT:{goto end;break;}case SDL_MOUSEBUTTONUP:{showClick(event,renderer,texture);break;}}}end:SDL_DestroyRenderer(renderer);SDL_DestroyTexture(texture);SDL_DestroyWindow(window);SDL_Quit();//初始化子系统后必须做一个退出操作
}SDL_Texture *playThread::createTexture(SDL_Renderer *renderer)
{//创建一个纹理对象SDL_Texture *texture = SDL_CreateTexture(renderer,SDL_PIXELFORMAT_RGB24,SDL_TEXTUREACCESS_TARGET,50,50);if(!texture){//创建失败return nullptr;}//设置纹理为渲染目标if(SDL_SetRenderTarget(renderer,texture)){return nullptr;}//设置颜色if(SDL_SetRenderDrawColor(renderer,255,255,0,SDL_ALPHA_OPAQUE)){return nullptr;}//画图形SDL_Rect rect = {0,0,50,50};if(SDL_RenderDrawRect(renderer,&rect)){return nullptr;}if(SDL_RenderDrawLine(renderer,0,0,50,50)){return nullptr;}if(SDL_RenderDrawLine(renderer,50,0,0,50)){return nullptr;}return texture;
}void playThread::showClick(SDL_Event &event, SDL_Renderer *renderer,SDL_Texture *texture)
{SDL_MouseButtonEvent btn = event.button;int w = 0,h = 0;if(SDL_QueryTexture(texture,nullptr,nullptr,&w,&h)){return;}int x = btn.x - (w >> 1);int y = btn.y - (h >> 1);SDL_Rect dstRect = {x,y,w,h};//SDL_RenderClear(renderer);//赋值纹理到渲染目标SDL_RenderCopy(renderer,texture,nullptr,&dstRect);//更新渲染操作到屏幕上SDL_RenderPresent(renderer);
}