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hack around DX texture problem

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This commit is contained in:
David Rose 2002-09-04 02:17:02 +00:00
parent bbd8b2a343
commit b41f230f44
1 changed files with 26 additions and 2 deletions
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28
panda/src/pgraph/cullResult.cxx
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@ -23,6 +23,30 @@
#include "renderState.h"
#include "clockObject.h"
// This value is used instead of 1.0 to represent the alpha level of a
// pixel that is to be considered "opaque" for the purposes of M_dual.
// Ideally, 1.0 is the only correct value for this. Realistically, we
// have to fudge it lower for two reasons:
// (1) The modelers tend to paint textures with very slight
// transparency levels in places that are not intended to be
// transparent, without realizing it. These very faint transparency
// regions are normally (almost) invisible, but when rendered with
// M_dual they may be revealed as regions of poor alpha sorting.
// (2) There seems to be some problem in DX where, in certain
// circumstances apparently related to automatic texture management,
// it spontaneously drops out the bottom two bits of an eight-bit
// alpha channel, causing a value of 255 to become a value of 252
// instead.
// We use 256 as the denominator here (instead of, say, 255) because a
// fractional power of two will have a terminating representation in
// base 2, and thus will be more likely to have a precise value in
// whatever internal representation the graphics API will use.
static const float dual_opaque_level = 252.0f / 256.0f;
////////////////////////////////////////////////////////////////////
// Function: CullResult::make_next
// Access: Public
@ -274,7 +298,7 @@ get_dual_transparent_state_decals() {
// test of < 1.0 instead of > 0.0. This makes us draw big empty
// pixels where the alpha values are 0.0, but we don't overwrite
// the decals where the pixels are 1.0.
state = RenderState::make(AlphaTestAttrib::make(AlphaTestAttrib::M_less, 1.0f),
state = RenderState::make(AlphaTestAttrib::make(AlphaTestAttrib::M_less, dual_opaque_level),
TransparencyAttrib::make(TransparencyAttrib::M_alpha),
RenderState::get_max_priority());
}
@ -305,7 +329,7 @@ CPT(RenderState) CullResult::
get_dual_opaque_state() {
static CPT(RenderState) state = NULL;
if (state == (const RenderState *)NULL) {
state = RenderState::make(AlphaTestAttrib::make(AlphaTestAttrib::M_equal, 1.0f),
state = RenderState::make(AlphaTestAttrib::make(AlphaTestAttrib::M_greater_equal, dual_opaque_level),
TransparencyAttrib::make(TransparencyAttrib::M_none),
RenderState::get_max_priority());
}