Re: [Mesa3d-dev] OSMesaMakeCurrent quickie

[Brian P. <br...@tu...>]

Eric Plante wrote:
> 
> Sorry, this is probably a silly question, I feel like I'm in the mood
> for missing completely obvious stuff...
> 
> With OSMesa-16, I suppose that the following comment does not apply
> (this is in osmesa.h from 4.0.1)
>   * Since the only type initially supported is GL_UNSIGNED_BYTE, if the
>   * context is in RGBA mode, each pixel will be stored as a 4-byte RGBA
>   * value.  If the context is in color indexed mode, each pixel will be
>   * stored as a 1-byte value.
> 
> This is a comment appearing for OSMesaMakeCurrent. What should I pass as
> the "type" parameter for OSMesa16? GL_UNSIGNED_INT? And how should I
> expect the memory to be laid out? 4 bytes / channel for a total of 16
> bytes / channel in RGBA?

The comment is dated.  I'm about to check in the following update:

/*
 * Bind an OSMesaContext to an image buffer.  The image buffer is just a
 * block of memory which the client provides.  Its size must be at least
 * as large as width*height*sizeof(type).  Its address should be a multiple
 * of 4 if using RGBA mode.
 *
 * Image data is stored in the order of glDrawPixels:  row-major order
 * with the lower-left image pixel stored in the first array position
 * (ie. bottom-to-top).
 *
 * If the context's viewport hasn't been initialized yet, it will now be
 * initialized to (0,0,width,height).
 *
 * Input:  ctx - the rendering context
 *         buffer - the image buffer memory
 *         type - data type for pixel components
 *            Normally, only GL_UNSIGNED_BYTE and GL_UNSIGNED_SHORT_5_6_5
 *            are supported.  But if Mesa's been compiled with CHAN_BITS==16
 *            then type must be GL_UNSIGNED_SHORT.  And if Mesa's been build
 *            with CHAN_BITS==32 then type must be GL_FLOAT.
 *         width, height - size of image buffer in pixels, at least 1
 * Return:  GL_TRUE if success, GL_FALSE if error because of invalid ctx,
 *          invalid buffer address, invalid type, width<1, height<1,
 *          width>internal limit or height>internal limit.
 */


For OSMesa16 (16 bits / channel) you'll have 8 bytes per pixel.  Color
channels are GLushorts.

For OSMesa32 (32 bits / channel) you'll have 16 bytes per pixel.  Color
channels are GLfloats.

-Brian