mesa: Mostly fix swrast's ARB_depth_clamp support.

I'd written a testcase for the hard part of the extension enablement, so
naturally the easy stuff was completely broken.  There are still issues,
as I'm seeing FLOAT_TO_UINT(max_f) == 0x0 when max_f == 1.0, but it gets
piglit depth-clamp-range closer to success.

2 files changed, 26 insertions, 12 deletions

diff --git a/src/mesa/swrast/s_depth.c b/src/mesa/swrast/s_depth.c
index 393590c673..c37a54eb3e 100644
--- a/src/mesa/swrast/s_depth.c
+++ b/src/mesa/swrast/s_depth.c
@@ -506,22 +506,32 @@ _swrast_depth_clamp_span( GLcontext *ctx, SWspan *span )
    struct gl_renderbuffer *rb = fb->_DepthBuffer;
    const GLuint count = span->end;
    GLuint *zValues = span->array->z;
-   GLuint near, far;
+   GLuint min, max;
+   GLfloat min_f, max_f;
    int i;
 
+   if (ctx->Viewport.Near < ctx->Viewport.Far) {
+      min_f = ctx->Viewport.Near;
+      max_f = ctx->Viewport.Far;
+   } else {
+      min_f = ctx->Viewport.Far;
+      max_f = ctx->Viewport.Near;
+   }
+
    if (rb->DataType == GL_UNSIGNED_SHORT) {
-      near = FLOAT_TO_UINT(ctx->Viewport.Near);
-      far = FLOAT_TO_UINT(ctx->Viewport.Far);
+      CLAMPED_FLOAT_TO_USHORT(min, min_f);
+      CLAMPED_FLOAT_TO_USHORT(max, max_f);
    } else {
       assert(rb->DataType == GL_UNSIGNED_INT);
-      CLAMPED_FLOAT_TO_USHORT(near, ctx->Viewport.Near);
-      CLAMPED_FLOAT_TO_USHORT(far, ctx->Viewport.Far);
+      min = FLOAT_TO_UINT(min_f);
+      max = FLOAT_TO_UINT(max_f);
    }
+
    for (i = 0; i < count; i++) {
-      if (zValues[i] < near)
-	 zValues[i] = near;
-      if (zValues[i] > far)
-	 zValues[i] = far;
+      if (zValues[i] < min)
+	 zValues[i] = min;
+      if (zValues[i] > max)
+	 zValues[i] = max;
    }
 }
 
diff --git a/src/mesa/swrast/s_span.c b/src/mesa/swrast/s_span.c
index 704230d1d7..d36c8132f6 100644
--- a/src/mesa/swrast/s_span.c
+++ b/src/mesa/swrast/s_span.c
@@ -880,14 +880,14 @@ _swrast_write_index_span( GLcontext *ctx, SWspan *span)
       stipple_polygon_span(ctx, span);
    }
 
-   if (ctx->Transform.DepthClamp)
-      _swrast_depth_clamp_span(ctx, span);
-
    /* Stencil and Z testing */
    if (ctx->Stencil._Enabled || ctx->Depth.Test) {
       if (!(span->arrayMask & SPAN_Z))
          _swrast_span_interpolate_z(ctx, span);
 
+      if (ctx->Transform.DepthClamp)
+	 _swrast_depth_clamp_span(ctx, span);
+
       if (ctx->Stencil._Enabled) {
          if (!_swrast_stencil_and_ztest_span(ctx, span)) {
             span->arrayMask = origArrayMask;
@@ -1356,6 +1356,10 @@ _swrast_write_rgba_span( GLcontext *ctx, SWspan *span)
    if (ctx->Stencil._Enabled || ctx->Depth.Test) {
       if (!(span->arrayMask & SPAN_Z))
          _swrast_span_interpolate_z(ctx, span);
+
+      if (ctx->Transform.DepthClamp)
+	 _swrast_depth_clamp_span(ctx, span);
+
       if (ctx->Stencil._Enabled) {
          /* Combined Z/stencil tests */
          if (!_swrast_stencil_and_ztest_span(ctx, span)) {