Mesa (master): llvmpipe: abstract the code to set number of subpixel bits

[Zack Rusin]

Module: Mesa
Branch: master
Commit: edde6c77bd1cb91f6f7c42010919e6f406f507ce
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=edde6c77bd1cb91f6f7c42010919e6f406f507ce

Author: Zack Rusin <zackr at vmware.com>
Date:   Wed Sep 25 19:38:33 2013 -0400

llvmpipe: abstract the code to set number of subpixel bits

As we're moving towards expanding the number of subpixel
bits and the width of the variables used in the computations
we need to make this code a bit more centralized.

Signed-off-by: Zack Rusin <zackr at vmware.com>
Reviewed-by: José Fonseca <jfonseca at vmware.com>
Reviewed-by: Brian Paul <brianp at vmware.com>

---

 src/gallium/drivers/llvmpipe/lp_rast.h      |    9 +++++++++
 src/gallium/drivers/llvmpipe/lp_setup.c     |   14 +++++---------
 src/gallium/drivers/llvmpipe/lp_setup_tri.c |    2 +-
 3 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/src/gallium/drivers/llvmpipe/lp_rast.h b/src/gallium/drivers/llvmpipe/lp_rast.h
index c57f2ea..43c598d 100644
--- a/src/gallium/drivers/llvmpipe/lp_rast.h
+++ b/src/gallium/drivers/llvmpipe/lp_rast.h
@@ -46,9 +46,18 @@ struct lp_scene;
 struct lp_fence;
 struct cmd_bin;
 
+#define FIXED_TYPE_WIDTH 32
 /** For sub-pixel positioning */
 #define FIXED_ORDER 4
 #define FIXED_ONE (1<<FIXED_ORDER)
+/** Maximum length of an edge in a primitive in pixels.
+ *  If the framebuffer is large we have to think about fixed-point
+ *  integer overflow. Coordinates need ((FIXED_TYPE_WIDTH/2) - 1) bits
+ *  to be able to fit product of two such coordinates inside
+ *  FIXED_TYPE_WIDTH, any larger and we could overflow a
+ *  FIXED_TYPE_WIDTH_-bit int.
+ */
+#define MAX_FIXED_LENGTH (1 << (((FIXED_TYPE_WIDTH/2) - 1) - FIXED_ORDER))
 
 /* Rasterizer output size going to jit fs, width/height */
 #define LP_RASTER_BLOCK_SIZE 4
diff --git a/src/gallium/drivers/llvmpipe/lp_setup.c b/src/gallium/drivers/llvmpipe/lp_setup.c
index c8199b4..9b277d3 100644
--- a/src/gallium/drivers/llvmpipe/lp_setup.c
+++ b/src/gallium/drivers/llvmpipe/lp_setup.c
@@ -1007,16 +1007,12 @@ try_update_scene_state( struct lp_setup_context *setup )
                                          &setup->draw_regions[i]);
          }
       }
-      /* If the framebuffer is large we have to think about fixed-point
-       * integer overflow.  For 2K by 2K images, coordinates need 15 bits
-       * (2^11 + 4 subpixel bits).  The product of two such numbers would
-       * use 30 bits.  Any larger and we could overflow a 32-bit int.
-       *
-       * To cope with this problem we check if triangles are large and
-       * subdivide them if needed.
+      /*
+       * Subdivide triangles if the framebuffer is larger than the
+       * MAX_FIXED_LENGTH.
        */
-      setup->subdivide_large_triangles = (setup->fb.width > 2048 ||
-                                          setup->fb.height > 2048);
+      setup->subdivide_large_triangles = (setup->fb.width > MAX_FIXED_LENGTH ||
+                                          setup->fb.height > MAX_FIXED_LENGTH);
    }
                                       
    setup->dirty = 0;
diff --git a/src/gallium/drivers/llvmpipe/lp_setup_tri.c b/src/gallium/drivers/llvmpipe/lp_setup_tri.c
index 051ffa0..2164f3a 100644
--- a/src/gallium/drivers/llvmpipe/lp_setup_tri.c
+++ b/src/gallium/drivers/llvmpipe/lp_setup_tri.c
@@ -988,7 +988,7 @@ check_subdivide_triangle(struct lp_setup_context *setup,
                          const float (*v2)[4],
                          triangle_func_t tri)
 {
-   const float maxLen = 2048.0f;  /* longest permissible edge, in pixels */
+   const float maxLen = (float) MAX_FIXED_LENGTH;  /* longest permissible edge, in pixels */
    float dx10, dy10, len10;
    float dx21, dy21, len21;
    float dx02, dy02, len02;