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mesa: Use GLdouble for depthMax in final unpack conversions.

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The final step of _mesa_unpack_depth_span is to take the temporary
GLfloat depth values and convert them to the desired format.  When
converting to GL_UNSIGNED_INTEGER with depthMax > 0xffffff, we use
double-precision math to avoid overflow and precision problems.

Or at least that's the idea.  Unfortunately

   GLdouble z = depthValues[i] * (GLfloat) depthMax;

actually causes single-precision multiplication, since both operands are
GLfloats.  Casting depthMax to GLdouble causes the scaling to be done
with double-precision math.

Fixes a regression in oglconform's depth-stencil basic.read.ds test
since c60ac7b179, where the expected and
actual values differed slightly.  For example, 0xcfa7a6 vs. 0xcfa7a4.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=49772
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
This commit is contained in:
Kenneth Graunke 2012-08-13 00:35:41 -07:00
parent 36fe8a5b7f
commit 57295009e8
1 changed files with 1 additions and 1 deletions
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2
src/mesa/main/pack.c
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@ -4900,7 +4900,7 @@ _mesa_unpack_depth_span( struct gl_context *ctx, GLuint n,
else {
/* need to use double precision to prevent overflow problems */
for (i = 0; i < n; i++) {
GLdouble z = depthValues[i] * (GLfloat) depthMax;
GLdouble z = depthValues[i] * (GLdouble) depthMax;
if (z >= (GLdouble) 0xffffffff)
zValues[i] = 0xffffffff;
else