Added support for floating point depth buffers on Savage4-based

hardware. By also reversing the depth range this can compensate the loss
of accuracy of far objects caused by the projective transformation.
Software fallbacks work but are slightly slower since floats in a custom
(non IEEE) format have to be encoded and decoded. I havn't done anything
about polygon offsets yet. There doesn't seem to be an easy way do get
it right except making the offset unit as big as the lowest resolution
of depth values. For now float depth is disabled by default but can be
enabled through driconf (though I have seen only positive effects so
far).

1 files changed, 30 insertions, 15 deletions

diff --git a/src/mesa/drivers/dri/savage/savagestate.c b/src/mesa/drivers/dri/savage/savagestate.c
index d6048291be..ec3b5c4adc 100644
--- a/src/mesa/drivers/dri/savage/savagestate.c
+++ b/src/mesa/drivers/dri/savage/savagestate.c
@@ -470,14 +470,14 @@ static void savageDDDepthFunc_s4(GLcontext *ctx, GLenum func)
      * set up z read/write watermarks register (global)
      */
 
-    switch(func)  { 
+    switch(func)  { /* reversed (see savageCalcViewport) */
     case GL_NEVER: zmode = CF_Never; break;
     case GL_ALWAYS: zmode = CF_Always; break;
-    case GL_LESS: zmode = CF_Less; break; 
-    case GL_LEQUAL: zmode = CF_LessEqual; break;
+    case GL_LESS: zmode = CF_Greater; break; 
+    case GL_LEQUAL: zmode = CF_GreaterEqual; break;
     case GL_EQUAL: zmode = CF_Equal; break;
-    case GL_GREATER: zmode = CF_Greater; break;
-    case GL_GEQUAL: zmode = CF_GreaterEqual; break;
+    case GL_GREATER: zmode = CF_Less; break;
+    case GL_GEQUAL: zmode = CF_LessEqual; break;
     case GL_NOTEQUAL: zmode = CF_NotEqual; break;
     default:return;
     } 
@@ -539,14 +539,14 @@ static void savageDDDepthFunc_s3d(GLcontext *ctx, GLenum func)
      * set up z-buffer offset register (global)
      * set up z read/write watermarks register (global)
      */
-    switch(func)  { 
+    switch(func)  { /* reversed (see savageCalcViewport) */
     case GL_NEVER: zmode = CF_Never; break;
     case GL_ALWAYS: zmode = CF_Always; break;
-    case GL_LESS: zmode = CF_Less; break; 
-    case GL_LEQUAL: zmode = CF_LessEqual; break;
+    case GL_LESS: zmode = CF_Greater; break; 
+    case GL_LEQUAL: zmode = CF_GreaterEqual; break;
     case GL_EQUAL: zmode = CF_Equal; break;
-    case GL_GREATER: zmode = CF_Greater; break;
-    case GL_GEQUAL: zmode = CF_GreaterEqual; break;
+    case GL_GREATER: zmode = CF_Less; break;
+    case GL_GEQUAL: zmode = CF_LessEqual; break;
     case GL_NOTEQUAL: zmode = CF_NotEqual; break;
     default:return;
     } 
@@ -716,14 +716,22 @@ static void savageCalcViewport( GLcontext *ctx )
    const GLfloat *v = ctx->Viewport._WindowMap.m;
    GLfloat *m = imesa->hw_viewport;
 
-   /* See also mga_translate_vertex.
-    */
    m[MAT_SX] =   v[MAT_SX];
    m[MAT_TX] =   v[MAT_TX] + imesa->drawX + SUBPIXEL_X;
    m[MAT_SY] = - v[MAT_SY];
    m[MAT_TY] = - v[MAT_TY] + imesa->driDrawable->h + imesa->drawY + SUBPIXEL_Y;
-   m[MAT_SZ] =   v[MAT_SZ] * imesa->depth_scale;
-   m[MAT_TZ] =   v[MAT_TZ] * imesa->depth_scale;
+   /* Depth range is reversed (far: 0, near: 1) so that float depth
+    * compensates for loss of accuracy of far coordinates. */
+   if (imesa->float_depth && imesa->savageScreen->zpp == 2) {
+       /* The Savage 16-bit floating point depth format can't encode
+	* numbers < 2^-16. Make sure all depth values stay greater
+	* than that. */
+       m[MAT_SZ] = - v[MAT_SZ] * imesa->depth_scale * (65535.0/65536.0);
+       m[MAT_TZ] = 1.0 - v[MAT_TZ] * imesa->depth_scale * (65535.0/65536.0);
+   } else {
+       m[MAT_SZ] = - v[MAT_SZ] * imesa->depth_scale;
+       m[MAT_TZ] = 1.0 - v[MAT_TZ] * imesa->depth_scale;
+   }
 
    imesa->SetupNewInputs = ~0;
 }
@@ -1612,7 +1620,14 @@ static void savageDDInitState_s4( savageContextPtr imesa )
 
     imesa->regs.s4.zBufCtrl.ni.zCmpFunc = CF_Less;
     imesa->regs.s4.zBufCtrl.ni.wToZEn               = GL_TRUE;
-    /*imesa->regs.s4.ZBufCtrl.ni.floatZEn          = GL_TRUE;*/
+    if (imesa->float_depth) {
+	imesa->regs.s4.zBufCtrl.ni.zExpOffset =
+	    imesa->savageScreen->zpp == 2 ? 16 : 32;
+	imesa->regs.s4.zBufCtrl.ni.floatZEn = GL_TRUE;
+    } else {
+	imesa->regs.s4.zBufCtrl.ni.zExpOffset = 0;
+	imesa->regs.s4.zBufCtrl.ni.floatZEn = GL_FALSE;
+    }
     imesa->regs.s4.texBlendCtrl[0].ui            = TBC_NoTexMap;
     imesa->regs.s4.texBlendCtrl[1].ui            = TBC_NoTexMap1;
     imesa->regs.s4.drawCtrl0.ui         = 0;