svga: fix FBO / viewport bugs

When drawing to a FBO, the viewport wasn't always set correctly.  It
was fine in the usual case of the viewport dims matching the surface
dims but broken otherwise.  In particular, this was happening because
the viewport scale is negative for FBO rendering.

The piglit fbo-viewport test exercises this.

Reviewed-by: José Fonseca <jfonseca@vmware.com>

diff --git a/src/gallium/drivers/svga/svga_state_framebuffer.c b/src/gallium/drivers/svga/svga_state_framebuffer.c
index 3244023..402d5fe 100644 (file)
--- a/src/gallium/drivers/svga/svga_state_framebuffer.c
+++ b/src/gallium/drivers/svga/svga_state_framebuffer.c
@@ -175,6 +175,7 @@ emit_viewport( struct svga_context *svga,
    float range_max = 1.0;
    float flip = -1.0;
    boolean degenerate = FALSE;
+   boolean invertY = FALSE;
    enum pipe_error ret;
 
    float fb_width = svga->curr.framebuffer.width;
@@ -218,11 +219,12 @@ emit_viewport( struct svga_context *svga,
       fx =        viewport->scale[0] * 1.0 + viewport->translate[0];
    }
 
-   if (fh < 0) {
-      prescale.scale[1] *= -1.0;
-      prescale.translate[1] += -fh;
+   if (fh < 0.0) {
+      prescale.translate[1] = fh - 1 + fy * 2;
       fh = -fh;
-      fy = flip * viewport->scale[1] * 1.0 + viewport->translate[1];
+      fy -= fh;
+      prescale.scale[1] = -1.0;
+      invertY = TRUE;
    }
 
    if (fx < 0) {
@@ -233,7 +235,12 @@ emit_viewport( struct svga_context *svga,
    }
 
    if (fy < 0) {
-      prescale.translate[1] += fy;
+      if (invertY) {
+         prescale.translate[1] -= fy;
+      }
+      else {
+         prescale.translate[1] += fy;
+      }
       prescale.scale[1] *= fh / (fh + fy); 
       fh += fy;
       fy = 0;
@@ -249,8 +256,15 @@ emit_viewport( struct svga_context *svga,
 
    if (fy + fh > fb_height) {
       prescale.scale[1] *= fh / (fb_height - fy);
-      prescale.translate[1] -= fy * (fh / (fb_height - fy));
-      prescale.translate[1] += fy;
+      if (invertY) {
+         float in = fb_height - fy;       /* number of vp pixels inside view */
+         float out = fy + fh - fb_height; /* number of vp pixels out of view */
+         prescale.translate[1] += fy * out / in;
+      }
+      else {
+         prescale.translate[1] -= fy * (fh / (fb_height - fy));
+         prescale.translate[1] += fy;
+      }
       fh = fb_height - fy;
    }
 
@@ -307,6 +321,9 @@ emit_viewport( struct svga_context *svga,
          break;
       }
 
+      if (invertY)
+         adjust_y = -adjust_y;
+
       prescale.translate[0] += adjust_x;
       prescale.translate[1] += adjust_y;
       prescale.translate[2] = 0.5; /* D3D clip space */