Re: [AD] Bug with transparent ellipses

[Jon Rafkind <workmin@xxxxxxxxxx>]

Elias Pschernig wrote:
> On Sun, 2006-09-03 at 15:42 -0600, Trent Gamblin wrote:
>   
>> The following code segfaults in Linux with 4.2.0:
>>
>> #include <allegro.h>
>>
>> int main(void)
>> {
>>     allegro_init();
>>     set_gfx_mode(GFX_AUTODETECT_WINDOWED, 640, 480, 0, 0);
>>     BITMAP* bmp = create_bitmap(640, 480);
>>     drawing_mode(DRAW_MODE_TRANS, 0, 0, 0);
>>     ellipsefill(bmp, 0, 0, 10, 10, 0);
>>     drawing_mode(DRAW_MODE_SOLID, 0, 0, 0);
>>     destroy_bitmap(bmp);
>>     allegro_exit();
>>     return 0;
>> }
>>
>>
>> It looks like Allegro is not doing bounds checking, but it works fine if 
>> you remove
>> the drawing_mode calls. I haven't tested with other primitives. Also 
>> haven't tried this
>> 4.3 so this may be fixed already.
>>
>>     
>
> The docs say this:
> "In DRAW_MODE_TRANS, the global color_map table or truecolor blender
> functions are used to overlay pixels on top of the existing image. This
> must only be used after you have set up the color mapping table (for 256
> color modes) or blender functions (for truecolor modes). Because it
> involves reading as well as writing the bitmap memory, translucent
> drawing is very slow if you draw directly to video RAM, so wherever
> possible you should use a memory bitmap instead."
>
> So I'd say, you simply forgot to set up those tables/functions. We
> probably should ASSERT for that in debug mode though - I'll try to come
> up with a patch to add such an ASSERT.
>
>   
It shouldnt segfault if the color table hasnt been set up, the colors
would just be garbage. Likewise if the blender functions havent been set
up there should be some default. Im trying to find the actual line that
segfaults, though.