Re: [AD] [Alleg5][GFX] Format specification

[Elias Pschernig <elias@xxxxxxxxxx>]

On Fri, 2007-01-26 at 01:42 -0600, Robert Jr Ohannessian wrote:
> I'd like to propose an alternative way of specifying bitmap formats in 
> the new graphics API.
> 
> Currently, we have a bunch of enums ORed together:
> 
>   * Allegro supports several color spaces. The color space is
>   * specified by the following flags in the format parameter:
>   *   - AL_RGBA
>   *   - AL_RGB
>   *   - AL_PALETTE
>   *   - AL_YUV
>   *   - AL_LUMINANCE
>   *
>   * These flags select the color space but not the color depth. The depth
>   * is selected via one of the following flags, which are combined with
>   * a binary OR (|) with the previous ones:
>   *   - AL_COLOR_8
>   *   - AL_COLOR_8_8_I
>   *   - AL_COLOR_5_5_5       (==  AL_COLOR_15?)
>   *   - AL_COLOR_5_6_5       (==  AL_COLOR_16?)
>   *   - AL_COLOR_8_8_8       (==  AL_COLOR_24?)
>   *   - AL_COLOR_8_8_8_8     (==  AL_COLOR_32?)
>   *   - AL_COLOR_10_10_10
>   *   - AL_COLOR_10_10_10_2
>   *   - AL_COLOR_16_16_16
>   *   - AL_COLOR_16_16_16_16
>   *   - AL_COLOR_32_32_32
>   *   - AL_COLOR_32_32_32_32 (== AL_COLOR_128?)
>   *
>   * The color depth specification can be augmented by the following 
> flags, which
>   * are combined with a binray OR (|) with the previous ones:
>   *   - AL_COLOR_INTEGER
>   *   - AL_COLOR_FLOAT
> 
> 
> Instead, I'd like to move towards a more OpenGL-like system: There ought 
> to be 3 separate format identifiers: <internalformat>, <format> and <type>.
> 
> When creating a bitmap, users specify only an <internalformat>, which is 
> essentially a hint to Allegro as to what format to actually pick. The 
> list of internalformats is much more contrained than all the 
> possibilities available above. For example: AL_RGBA8, AL_RGB5_A1, or 
> AL_RGB32F, or even AL_YUV_422.
> 
> However, when data supplied directly by the user needs to be provided to 
> Allegro (ie: through al_bitmap_write*() and al_bitmap_read*()), then 
> separate <format> and <type> parameters can be queried so that users can 
> know how to provide the necessary information to Allegro.
> 
> For example, AL_RGB32F bitmaps would return a format of AL_RGB and a 
> type of AL_FLOAT32. Or perhaps a format of AL_BGR, on platforms where 
> the component ordering is reversed.
> 
> Writing the bitmap one pixel at a time, through al_put_pixel() / 
> al_make_rgb*() would still not need to know the bitmap format, from the 
> users' perspective.
> 
> I think the benefit here is reducing parameter validation complexity, 
> and format explosion.
> 
> Thoughts?
> 

I think it's a good idea.

I'm also planning to move the alleg.sf.net/future documents to the wiki,
should make it somewhat easier updating them. Right now, to e.g. remove
the al_blit_region_3(), you need to download the file, replace it, then
upload back over ssh.

-- 
Elias Pschernig