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 Post subject: Share code to draw using SDL
PostPosted: Tue Aug 08, 2017 3:37 pm 
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So far, I use Windows, and the MSYS 1.0 that comes with MinGW to compile.

I can compile this SDL skeleton (with SDL 1, most surely also with SDL 2):
Code:
#include <SDL.h>

int main( int argc, char* args[] )
{
//Start SDL
///
  SDL_Init( SDL_INIT_EVERYTHING );

//Quit SDL
///
  SDL_Quit();

return 0;
}




This video shows how to compile it:


Quote:
http://lazyfoo.net/SDL_tutorials/lesson01/windows/mingw/index.php

Download SDL 1:
https://www.libsdl.org/download-1.2.php

Commands:
SDLCFLAGS=$(sdl-config --cflags)
SDLLIBS=$(sdl-config --libs)
gcc HelloSDL.cpp -o HelloSDL.exe $SDLCFLAGS $SDLLIBS
HelloSDL.exe




Now I want to know how I can create a window and draw generic stuff, like pixels, to the SDL window.

Can you share some clear code so I can do that, just creating the SDL window and drawing in it?

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 Post subject: Re: Share code to draw using SDL
PostPosted: Tue Aug 08, 2017 6:16 pm 
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Joined: Sat Dec 27, 2014 9:11 am
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Location: Maadi, Cairo, Egypt
~ wrote:
Can you share some clear code so I can do that, just creating the SDL window and drawing in it?

The SDL documentation isn't that bad. Other SDL examples/tutorials aren't bad either and serve as a proper starting point.

Anyways...
Code:
SDL_Window *window;
SDL_Surface *surface;
uint32_t *framebuffer;      // pointer to raw pixel buffer that you can read/write

int init()
{
   // initialize the video subsystem
   if(SDL_Init(SDL_INIT_VIDEO) < 0)
      return 1;

   // make a window
   SDL_Window *window;
   window = SDL_CreateWindow("Window title", x_position, y_position, width, height, SDL_WINDOW_SHOWN);

   // ensure window handle is valid
   if(!window)
      return 1;

   // a surface is a group of pixels displayed on screen
   // return the window's surface
   SDL_Surface *surface;
   surface = SDL_GetWindowSurface(window);

   // ensure compatible surface
   // here, we're looking at a 32-bit little endian RGB buffer
   // basically, the bytes should be BB GG RR 00
   if(surface->format->BitsPerPixel != 32 || surface->format->BytesPerPixel != 4 || surface->format->Rmask != 0xFF0000 || surface->format->Gmask != 0x00FF00 || surface->format->Bmask != 0x0000FF)
      return 1;

   // set up the pointer to the framebuffer
   framebuffer = surface->pixels;

   while(1)
   {
      handle_events();
   }
}

// sample put pixel, assumes 32-bit little endian RGB as we verified above^^

void put_pixel(short x, short y, uint32_t color)
{
   // calculate pixel offsets just like any other graphics programming
   uint32_t *ptr = ((y * (width << 2)) + (x << 2) + framebuffer);

   // to modify pixels yourself, you need to lock the surface to be safe
   SDL_LockSurface(surface);

   ptr[0] = color;      // write the pixel

   // redraw
   SDL_UnlockSurface(surface);
   SDL_UpdateWindowSurface(window);
}



Notice the function "handle_events" must handle the SDL events. SDL, in my experience, doesn't let the window display any changes unless its events are being handled, which makes sense, really.

Of course, you don't need to verify a 32-bit little-endian RGB surface, but I just do it this way out of laziness. Instead, you can implement support for multiple surface formats, to ensure maximum compatibility.

EDIT: I'm not sure if this works for SDL1, as I only ever used SDL2.

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