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

[Thomas Fjellstrom <tfjellstrom@xxxxxxxxxx>]

On Friday 26 January 2007 12:42 am, 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?
>

Whatever makes things simpler for both the allegro developers and end users is 
ok in my books.

-- 
Thomas Fjellstrom
tfjellstrom@xxxxxxxxxx