C++ SDL2:如何将矩形渲染到多个视口中

Question

我是 SDL2(版本 2.0.10(的新手，我从 Lazy Foo 教程中教它。在视口示例代码的课程中，我只呈现左侧视口中的第一个图像，而其他图像则不然。在不同视口中渲染矩形也不起作用。当我想在不同的视口中渲染矩形时，我做错了什么，如下所示：

while( !quit ){
while( SDL_PollEvent( &e ) != 0 ){
if( e.type == SDL_QUIT ){
quit = true;
}
}
//Clear screen
SDL_SetRenderDrawColor( gRenderer, 0xFF, 0xFF, 0xFF, 0xFF );
SDL_RenderClear( gRenderer );
//Top left corner viewport
SDL_Rect topLeftViewport;
topLeftViewport.x = 0;
topLeftViewport.y = 0;
topLeftViewport.w = SCREEN_WIDTH / 2;
topLeftViewport.h = SCREEN_HEIGHT / 2;
SDL_RenderSetViewport( gRenderer, &topLeftViewport );
SDL_Rect fillRect = { 10, 10, 100, 100 };
SDL_SetRenderDrawColor( gRenderer, 0xFF, 0x00, 0x00, 0xFF );
SDL_RenderFillRect( gRenderer, &fillRect );
SDL_Rect topRightViewport;
topRightViewport.x = SCREEN_WIDTH / 2;
topRightViewport.y = 0;
topRightViewport.w = SCREEN_WIDTH / 2;
topRightViewport.h = SCREEN_HEIGHT / 2;
SDL_RenderSetViewport( gRenderer, &topRightViewport );
SDL_Rect fillRect2 = { 10, 10, 100, 100 };
SDL_SetRenderDrawColor( gRenderer, 0x00, 0xFF, 0x00, 0xFF );
SDL_RenderFillRect( gRenderer, &fillRect2 );
SDL_RenderPresent( gRenderer );
}

Answer 1

正如我所看到的，您两次在 10x100 的 100x100 处绘制一个矩形，此坐标没有考虑视口坐标。在某种程度上，如果您想通过更改视口剪切来做到这一点，则无关紧要......只需在您想要的地方绘制正方形即可。

更新：我尝试了多个视口。这是一个工作示例。您可以在渲染器(带视口(或经典方式之间进行选择。

主要.cpp ：

#include "Application.hpp"
int
main (int argc, char * argv[])
{
Application app("SDL 2 Test", 800, 600, true);
return app.mainLoop();
}

应用.hpp ：

#ifndef APPLICATION_HPP
#define APPLICATION_HPP
#include <SDL2/SDL.h>
class Application
{
public:
Application (const char * title = "UnknownApplication", int baseWidth = 640, int baseHeight = 480, bool useRenderer = false) noexcept;
~Application ();
int mainLoop () noexcept;
private:
int m_width = 0;
int m_height = 0;
SDL_Window * m_window = nullptr;
SDL_Renderer * m_renderer = nullptr;
bool m_useRenderer = false;
bool m_isRunning = false;
};
#endif /* APPLICATION_HPP */

应用.cpp ：

#include "Application.hpp"
#include <iostream>
#include <SDL2/SDL_image.h>
Application::Application (const char * title, int baseWidth, int baseHeight, bool useRenderer) noexcept
: m_width(baseWidth), m_height(baseHeight), m_useRenderer(useRenderer)
{
if ( SDL_Init(SDL_INIT_VIDEO) != 0 )
{
std::cerr << "SDL could not initialize! SDL_Error: " << SDL_GetError() << std::endl;
return;
}
m_window = SDL_CreateWindow(title, SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, m_width, m_height, SDL_WINDOW_SHOWN);
if ( m_window == nullptr )
{
std::cerr << "Window could not be created! SDL_Error: " << SDL_GetError() << std::endl;
return;
}
if ( m_useRenderer )
{
m_renderer = SDL_CreateRenderer(m_window, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC | SDL_RENDERER_TARGETTEXTURE);
if ( m_renderer == nullptr )
{
std::cerr << "Renderer could not be created! SDL_Error: " << SDL_GetError() << std::endl;
return;
}
}
m_isRunning = true;
}
int
Application::mainLoop () noexcept
{
SDL_Event event;
const auto filepath = "SET_IMAGE_YOU_WANT_HERE";
auto surface = IMG_Load(filepath);
if ( surface == nullptr )
{
std::cerr << "Unable to read image file : " << filepath << std::endl;
return 1;
}
SDL_Rect logoPosition = {8, 8, 32, 32};
if ( m_useRenderer )
{
auto texture = SDL_CreateTextureFromSurface(m_renderer, surface);
SDL_Rect screenA = {0, 0, m_width / 2, m_height / 2};
SDL_Rect screenB = {m_width / 2, 0, m_width / 2, m_height / 2};
while ( m_isRunning )
{
while ( SDL_PollEvent(&event) != 0 )
{
if ( event.type == SDL_QUIT )
m_isRunning = false;
}
SDL_SetRenderDrawColor(m_renderer, 0, 0, 0, 255);
SDL_RenderClear(m_renderer);
SDL_RenderSetViewport(m_renderer, &screenA);
SDL_SetRenderDrawColor(m_renderer, 255, 0, 0, 255);
SDL_RenderFillRect(m_renderer, nullptr);
SDL_RenderCopy(m_renderer, texture, nullptr, &logoPosition);
SDL_RenderSetViewport(m_renderer, &screenB);
SDL_SetRenderDrawColor(m_renderer, 0, 255, 0, 255);
SDL_RenderFillRect(m_renderer, nullptr);
SDL_RenderCopy(m_renderer, texture, nullptr, &logoPosition);
SDL_RenderPresent(m_renderer);
}
SDL_DestroyTexture(texture);
}
else
{
auto windowSurface = SDL_GetWindowSurface(m_window);
while ( m_isRunning )
{
while ( SDL_PollEvent(&event) != 0 )
{
if ( event.type == SDL_QUIT )
m_isRunning = false;
}
SDL_FillRect(windowSurface, nullptr, SDL_MapRGB(windowSurface->format, 0xFF, 0x00, 0xFF));
//SDL_BlitSurface(surface, nullptr, windowSurface, &logoPosition);
SDL_BlitScaled(surface, nullptr, windowSurface, &logoPosition);
SDL_UpdateWindowSurface(m_window);
}
}
SDL_FreeSurface(surface);
return 0;
}
Application::~Application (void)
{
if ( m_renderer != nullptr )
SDL_DestroyRenderer(m_renderer);
if ( m_window != nullptr )
SDL_DestroyWindow(m_window);
SDL_Quit();
}