SDL_Rect is larger than specified - c++

Question

I've gotten a weird error with SDL_Rect. Whenever I call SDL_RenderFillRect, with this rectangle:
SDL_Rect rect = {100, 100, 100, 100};
I always end up with the rectangle covering the entire 800 x 600 window.
Here's my program:
#include "SDL.h"
#include <iostream>
#include <cstdlib>
#include <ctime>
#include <thread>
#include <string>
class Window
{
public:
Window( std::string title, int width, int height );
void runEvents( SDL_Event event );
void drawRect( int x, int y, int h, int w );
bool closed = false;
SDL_Renderer *_renderer;
SDL_Window *_window;
private:
int colour = 0;
};
Window::Window( std::string title, int width, int height )
{
_window = SDL_CreateWindow( title.c_str(), SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, width, height, 0 );
_renderer = SDL_CreateRenderer( _window, -1, 0 );
}
// this function deals with rects (it's supposed to draw a rect when the mouse button is down):
void Window::runEvents( SDL_Event event )
{
SDL_Rect rect = { 100, 100, 100, 100 };
switch( event.type )
{
case SDL_QUIT:
closed = true;
break;
case SDL_KEYDOWN:
switch( event.key.keysym.sym )
{
case SDLK_ESCAPE:
closed = true;
break;
case SDLK_KP_1:
// set colour to blue
SDL_SetRenderDrawColor( _renderer, 0, 51, 204, 255 );
std::cout << "Colour set to blue!" << std::endl;
colour = 1;
break;
case SDLK_KP_2:
// set colour to red
SDL_SetRenderDrawColor( _renderer, 255, 0, 0, 255 );
std::cout << "Colour set to red!" << std::endl;
colour = 2;
break;
case SDLK_KP_3:
// set colour to green
SDL_SetRenderDrawColor( _renderer, 51, 204, 51, 255 );
std::cout << "Colour set to green!" << std::endl;
colour = 3;
break;
case SDLK_KP_4:
SDL_SetRenderDrawColor( _renderer, 153, 0, 153, 255 );
std::cout << "Colour set to purple!" << std::endl;
colour = 4;
break;
case SDLK_KP_0:
SDL_SetRenderDrawColor( _renderer, 255, 255, 255, 255 );
std::cout << "Colour set to white!" << std::endl;
colour = 0;
break;
}
break;
//this draws the rectangle:
case SDL_MOUSEBUTTONDOWN:
SDL_SetRenderDrawColor( _renderer, 255, 0, 0, 255 );
drawRect( rect.h, rect.y, rect.h, rect.w );
break;
//this removes it
case SDL_MOUSEBUTTONUP:
switch( colour )
{
case 1:
SDL_SetRenderDrawColor( _renderer, 0, 51, 204, 255 );
break;
case 2:
SDL_SetRenderDrawColor( _renderer, 255, 0, 0, 255 );
break;
case 3:
SDL_SetRenderDrawColor( _renderer, 51, 204, 51, 255 );
break;
case 4:
SDL_SetRenderDrawColor( _renderer, 153, 0, 153, 255 );
break;
case 0:
SDL_SetRenderDrawColor( _renderer, 255, 255, 255, 255 );
break;
}
drawRect( rect.h, rect.y, rect.h, rect.w );
break;
}
}
//this function is supposed to draw the rect
void Window::drawRect( int x, int y, int h, int w )
{
SDL_Rect rect = { x, y, w, h };
SDL_RenderFillRect( _renderer, &rect );
}
bool running = true;
void mouseCheck()
{
while( running )
{
int x;
int y;
SDL_GetMouseState( &x, &y );
printf( "Mouse is at x: %i and y: %i\n", x, y );
SDL_Delay( 5000 );
}
}
int main( int argc, char *argv[] )
{
SDL_Init( SDL_INIT_EVERYTHING );
Window window( "Hello World", 800, 600 );
SDL_Event event;
SDL_SetRenderDrawColor( window._renderer, 255, 255, 255, 255 );
std::thread mousePosition( mouseCheck );
mousePosition.detach();
while( !window.closed )
{
SDL_RenderClear( window._renderer );
SDL_RenderPresent( window._renderer );
if( SDL_PollEvent( &event ) )
{
window.runEvents( event );
}
}
return 0;
}

Answer 1

Multiple issues:
Right now your main draw loop is:
1. Draw
2. Clear
3. Present
You want:
1. (re)Set clear color
2. Clear
3. Draw
4. Present
Not sure what you're trying for with that mouseCheck() thread but avoid calling GUI-related SDL functions from other threads. If you need that info in another thread use thread-safe atomics/queues/messages to communicate it.
You're calling drawRect() in two places with rect.h as the first parameter instead of rect.x.
I'd recommend against interleaving input processing and rendering like you're doing in runEvents(). Update the system state (shouldDrawRect & colour) while draining the event queue (while(SDL_PollEvent())), then draw a frame with the new state (Window::drawScene()).
You're only processing a single event per frame. Drain the event queue each frame via while(SDL_PollEvent()) so that events don't get backed up and dropped.
All together:
#include "SDL.h"
#include <iostream>
#include <cstdlib>
#include <ctime>
#include <thread>
#include <string>
class Window
{
public:
Window( std::string title, int width, int height );
void runEvents( SDL_Event event );
void drawScene();
void drawRect( int x, int y, int h, int w );
bool closed = false;
SDL_Renderer *_renderer;
SDL_Window *_window;
private:
bool shouldDrawRect;
int colour = 0;
};
Window::Window( std::string title, int width, int height )
{
_window = SDL_CreateWindow( title.c_str(), SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, width, height, 0 );
_renderer = SDL_CreateRenderer( _window, -1, 0 );
shouldDrawRect = false;
}
void Window::drawScene()
{
if( shouldDrawRect )
{
switch( colour )
{
case 0:
SDL_SetRenderDrawColor( _renderer, 255, 0, 0, 255 );
break;
case 1:
SDL_SetRenderDrawColor( _renderer, 0, 51, 204, 255 );
break;
case 2:
SDL_SetRenderDrawColor( _renderer, 255, 0, 0, 255 );
break;
case 3:
SDL_SetRenderDrawColor( _renderer, 51, 204, 51, 255 );
break;
case 4:
SDL_SetRenderDrawColor( _renderer, 153, 0, 153, 255 );
break;
}
SDL_Rect rect = { 100, 100, 100, 100 };
drawRect( rect.x, rect.y, rect.h, rect.w );
}
}
//this function deals with rects (it's supposed to draw a rect when the mouse button is down):
void Window::runEvents( SDL_Event event )
{
switch( event.type )
{
case SDL_QUIT:
closed = true;
break;
case SDL_KEYDOWN:
switch( event.key.keysym.sym )
{
case SDLK_ESCAPE:
closed = true;
break;
case SDLK_KP_1:
// set colour to blue
std::cout << "Colour set to blue!" << std::endl;
colour = 1;
break;
case SDLK_KP_2:
// set colour to red
std::cout << "Colour set to red!" << std::endl;
colour = 2;
break;
case SDLK_KP_3:
// set colour to green
std::cout << "Colour set to green!" << std::endl;
colour = 3;
break;
case SDLK_KP_4:
std::cout << "Colour set to purple!" << std::endl;
colour = 4;
break;
case SDLK_KP_0:
std::cout << "Colour set to white!" << std::endl;
colour = 0;
break;
}
break;
//this draws the rectangle:
case SDL_MOUSEBUTTONDOWN:
shouldDrawRect = true;
break;
//this removes it
case SDL_MOUSEBUTTONUP:
shouldDrawRect = false;
break;
}
}
//this function is supposed to draw the rect
void Window::drawRect( int x, int y, int h, int w )
{
SDL_Rect rect = { x, y, w, h };
SDL_RenderFillRect( _renderer, &rect );
}
bool running = true;
int main( int argc, char *argv[] )
{
SDL_Init( SDL_INIT_EVERYTHING );
Window window( "Hello World", 800, 600 );
SDL_Event event;
while( !window.closed )
{
SDL_SetRenderDrawColor( window._renderer, 255, 255, 255, 255 );
SDL_RenderClear( window._renderer );
while( SDL_PollEvent( &event ) )
{
window.runEvents( event );
}
window.drawScene();
SDL_RenderPresent( window._renderer );
}
return 0;
}