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SDL_Rect ushort?

 
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DarthCthulhu



Joined: 25 Aug 2010
Posts: 1
PostPosted: Wed Aug 25, 2010 10:59 am    Post subject: SDL_Rect ushort? Reply with quote
Hey there.

Derelict is a truly awesome library and I absolutely love the D language. Recently, I encountered somewhat strange behavior, though; the SDL_Rect structure appears to be made of ushorts rather than ints. Is this by design?

I'm curious because one of the major uses of SDL_Rects is as clipping rectangles for textures, but the SDL_Surface .w and .h members are ints which means you can't set an SDL_Rect's members to that of a SDL_Surface without an explicit cast to ushort.
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mutable



Joined: 22 Jun 2010
Posts: 87
PostPosted: Wed Aug 25, 2010 12:08 pm    Post subject: Reply with quote
On the SDL reference you can see this:
Code:

typedef struct{
  Sint16 x, y;
  Uint16 w, h;
} SDL_Rect;

and as you can see in the sdltypes.d file:
Code:

alias ubyte Uint8;
alias byte Sint8;
alias ushort Uint16;
alias short Sint16;

are x and y short and w and h are ushort.
Also you must cast like this:
Code:
SDL_Rect rect;
rect.x = cast(short) 180;
rect.y = cast(short) 200;
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aldacron



Joined: 05 May 2004
Posts: 1322
Location: Seoul, South Korea
PostPosted: Wed Aug 25, 2010 8:05 pm    Post subject: Re: SDL_Rect ushort? Reply with quote
DarthCthulhu wrote:
Hey there.

Derelict is a truly awesome library and I absolutely love the D language. Recently, I encountered somewhat strange behavior, though; the SDL_Rect structure appears to be made of ushorts rather than ints. Is this by design?

I'm curious because one of the major uses of SDL_Rects is as clipping rectangles for textures, but the SDL_Surface .w and .h members are ints which means you can't set an SDL_Rect's members to that of a SDL_Surface without an explicit cast to ushort.


As mutable mentioned above, the SDL C headers declare 16-bit integers for the SDL_Rect fields. There's no choice but to use short/ushort on the D side, otherwise it's not binary compatible with the C library.

In C, you can go from bigger integers to smaller integers (like int to short) without casting. However, this can truncate larger values and cause silent bugs that are hard to track down. A part of Walter's philosophy with D is that it should avoid known causes of silent bugs. Therefore, we have to explicitly cast from int to short.
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