added a note about the Creative Technology Ltd patent (US Patent #6384822) on the...

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@3675 d7cf8633-e32d-0410-b094-e92efae38249

diff --git a/r_shadow.c b/r_shadow.c
index 01e0c30815a461b6bd0b88cd85b2eff83ed6f79b..5d0965a2adc777ba0f62e2e897a76f07dd419009 100644 (file)
--- a/r_shadow.c
+++ b/r_shadow.c
@@ -14,7 +14,16 @@ did not intersect the visible geometry, suitable as a stencil mask for
 rendering lighting everywhere but shadow.
 
 In our case we use a biased stencil clear of 128 to avoid requiring the
-stencil wrap extension (but probably should support it).
+stencil wrap extension (but probably should support it), and to address
+Creative's patent on this sort of technology we also draw the frontfaces
+first, and backfaces second (decrement, increment).
+
+Patent warning:
+This algorithm may be covered by Creative's patent (US Patent #6384822)
+on Carmack's Reverse paper (which I have not read), however that patent
+seems to be about drawing a stencil shadow from a model in an otherwise
+unshadowed scene, where as realtime lighting technology draws light where
+shadows do not lie.
 
 
 
@@ -626,15 +635,15 @@ void R_Shadow_Volume(int numverts, int numtris, const float *invertex3f, int *el
                GL_VertexPointer(varray_vertex3f2);
                if (r_shadowstage == SHADOWSTAGE_STENCIL)
                {
-                       // increment stencil if backface is behind depthbuffer
-                       qglCullFace(GL_BACK); // quake is backwards, this culls front faces
-                       qglStencilOp(GL_KEEP, GL_INCR, GL_KEEP);
-                       R_Mesh_Draw(outverts, tris, shadowelements);
-                       c_rt_shadowmeshes++;
-                       c_rt_shadowtris += numtris;
                        // decrement stencil if frontface is behind depthbuffer
                        qglCullFace(GL_FRONT); // quake is backwards, this culls back faces
                        qglStencilOp(GL_KEEP, GL_DECR, GL_KEEP);
+                       R_Mesh_Draw(outverts, tris, shadowelements);
+                       c_rt_shadowmeshes++;
+                       c_rt_shadowtris += numtris;
+                       // increment stencil if backface is behind depthbuffer
+                       qglCullFace(GL_BACK); // quake is backwards, this culls front faces
+                       qglStencilOp(GL_KEEP, GL_INCR, GL_KEEP);
                }
                R_Mesh_Draw(outverts, tris, shadowelements);
                c_rt_shadowmeshes++;
@@ -647,9 +656,9 @@ void R_Shadow_RenderShadowMeshVolume(shadowmesh_t *firstmesh)
        shadowmesh_t *mesh;
        if (r_shadowstage == SHADOWSTAGE_STENCIL)
        {
-               // increment stencil if backface is behind depthbuffer
-               qglCullFace(GL_BACK); // quake is backwards, this culls front faces
-               qglStencilOp(GL_KEEP, GL_INCR, GL_KEEP);
+               // decrement stencil if frontface is behind depthbuffer
+               qglCullFace(GL_FRONT); // quake is backwards, this culls back faces
+               qglStencilOp(GL_KEEP, GL_DECR, GL_KEEP);
                for (mesh = firstmesh;mesh;mesh = mesh->next)
                {
                        GL_VertexPointer(mesh->vertex3f);
@@ -657,9 +666,9 @@ void R_Shadow_RenderShadowMeshVolume(shadowmesh_t *firstmesh)
                        c_rtcached_shadowmeshes++;
                        c_rtcached_shadowtris += mesh->numtriangles;
                }
-               // decrement stencil if frontface is behind depthbuffer
-               qglCullFace(GL_FRONT); // quake is backwards, this culls back faces
-               qglStencilOp(GL_KEEP, GL_DECR, GL_KEEP);
+               // increment stencil if backface is behind depthbuffer
+               qglCullFace(GL_BACK); // quake is backwards, this culls front faces
+               qglStencilOp(GL_KEEP, GL_INCR, GL_KEEP);
        }
        for (mesh = firstmesh;mesh;mesh = mesh->next)
        {
@@ -818,6 +827,7 @@ void R_Shadow_Stage_Begin(void)
        GL_DepthTest(true);
        R_Mesh_State_Texture(&m);
        GL_Color(0, 0, 0, 1);
+       qglCullFace(GL_FRONT); // quake is backwards, this culls back faces
        qglDisable(GL_SCISSOR_TEST);
        r_shadowstage = SHADOWSTAGE_NONE;
 
@@ -860,6 +870,7 @@ void R_Shadow_Stage_ShadowVolumes(void)
        else
                qglDisable(GL_POLYGON_OFFSET_FILL);
        qglDepthFunc(GL_LESS);
+       qglCullFace(GL_FRONT); // quake is backwards, this culls back faces
        qglEnable(GL_STENCIL_TEST);
        qglStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
        qglStencilFunc(GL_ALWAYS, 128, 0xFF);
@@ -887,6 +898,7 @@ void R_Shadow_Stage_LightWithoutShadows(void)
        GL_Color(1, 1, 1, 1);
        qglColorMask(1, 1, 1, 1);
        qglDepthFunc(GL_EQUAL);
+       qglCullFace(GL_FRONT); // quake is backwards, this culls back faces
        qglDisable(GL_STENCIL_TEST);
        qglStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
        qglStencilFunc(GL_EQUAL, 128, 0xFF);
@@ -906,6 +918,7 @@ void R_Shadow_Stage_LightWithShadows(void)
        GL_Color(1, 1, 1, 1);
        qglColorMask(1, 1, 1, 1);
        qglDepthFunc(GL_EQUAL);
+       qglCullFace(GL_FRONT); // quake is backwards, this culls back faces
        qglEnable(GL_STENCIL_TEST);
        qglStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
        // only draw light where this geometry was already rendered AND the
@@ -928,6 +941,7 @@ void R_Shadow_Stage_End(void)
        qglColorMask(1, 1, 1, 1);
        qglDisable(GL_SCISSOR_TEST);
        qglDepthFunc(GL_LEQUAL);
+       qglCullFace(GL_FRONT); // quake is backwards, this culls back faces
        qglDisable(GL_STENCIL_TEST);
        qglStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
        qglStencilFunc(GL_ALWAYS, 128, 0xFF);