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wined3d: Rewrite the comment in compute_texture_matrix().

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Make the function easier to understand, and use language that's a little less
GL-centric.
This commit is contained in:
Elizabeth Figura 2024-10-31 21:50:47 -05:00 committed by Alexandre Julliard
parent 70258a160f
commit f588fec26c
Notes: Alexandre Julliard 2024-11-13 22:30:11 +01:00 
Approved-by: Jan Sikorski (@jsikorski)
Approved-by: Alexandre Julliard (@julliard)
Merge-Request: https://gitlab.winehq.org/wine/wine/merge_requests/6756
1 changed files with 20 additions and 15 deletions
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35
dlls/wined3d/utils.c
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@ -5608,38 +5608,43 @@ static void compute_texture_matrix(const struct wined3d_matrix *matrix, uint32_t
mat = *matrix;
/* Under Direct3D the R/Z coord can be used for translation, under
* OpenGL we use the Q coord instead. */
/* When less than 4 components are provided for an attribute, the remaining
* components are filled with (..., 0, 0, 1). This is the case when using
* shaders in Direct3D as well as in GL and Vulkan.
*
* However, when using the Direct3D fixed function vertex pipeline, the
* texture coordinates transformed by texture matrices effectively have
* 1 in the first "default" component and 0 in the others (e.g. for
* R32_FLOAT the coordinates are (..., 1, 0, 0).
*
* We could approximate this by modifying the shader, but modifying uniforms
* is generally cheaper, so instead we change the matrix, copying the 2nd or
* 3rd column to the 4th. That is, whichever coefficients expect a value of
* 1 will instead be used as the coefficients for the 4th column, which
* actually has a value of 1. The coefficients for other columns don't need
* to be modified, since the corresponding texcoord components are zero. */
if (!(flags & WINED3D_TTFF_PROJECTED) && !calculated_coords)
{
switch (format_id)
{
/* Direct3D passes the default 1.0 in the 2nd coord, while GL
* passes it in the 4th. Swap 2nd and 4th coord. No need to
* store the value of mat._41 in mat._21 because the input
* value to the transformation will be 0, so the matrix value
* is irrelevant. */
case WINED3DFMT_R32_FLOAT:
mat._41 = mat._21;
mat._42 = mat._22;
mat._43 = mat._23;
mat._44 = mat._24;
break;
/* See above, just 3rd and 4th coord. */
case WINED3DFMT_R32G32_FLOAT:
mat._41 = mat._31;
mat._42 = mat._32;
mat._43 = mat._33;
mat._44 = mat._34;
break;
case WINED3DFMT_R32G32B32_FLOAT: /* Opengl defaults match dx defaults */
case WINED3DFMT_R32G32B32A32_FLOAT: /* No defaults apply, all app defined */
/* This is to prevent swapping the matrix lines and put the default 4th coord = 1.0
* into a bad place. The division elimination below will apply to make sure the
* 1.0 doesn't do anything bad. The caller will set this value if the stride is 0
*/
case WINED3DFMT_UNKNOWN: /* No texture coords, 0/0/0/1 defaults are passed */
case WINED3DFMT_R32G32B32_FLOAT:
case WINED3DFMT_R32G32B32A32_FLOAT:
case WINED3DFMT_UNKNOWN:
break;
default:
FIXME("Unexpected fixed function texture coord input\n");