intel: Refactor intel_mipmap_level offsets

Add a new field, intel_mipmap_level::slice, and move the offset fields
into it. Also add some much needed documentation for these fields.

Before this patch, a separate array was allocated for the
intel_mipmap_level::{x,y}_offsets.  This was just silly; it incurred an
extra call to malloc and diminished memory locality.

Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Chad Versace <chad.versace@linux.intel.com>

src/mesa/drivers/dri/intel/intel_mipmap_tree.c

@@ -226,8 +226,7 @@ intel_miptree_release(struct intel_mipmap_tree **mt)
       intel_region_release(&((*mt)->hiz_region));
 
       for (i = 0; i < MAX_TEXTURE_LEVELS; i++) {
-	 free((*mt)->level[i].x_offset);
-	 free((*mt)->level[i].y_offset);
+	 free((*mt)->level[i].slice);
       }
 
       free(*mt);
@@ -303,12 +302,11 @@ intel_miptree_set_level_info(struct intel_mipmap_tree *mt,
        level, w, h, d, x, y);
 
    assert(nr_images);
-   assert(!mt->level[level].x_offset);
+   assert(mt->level[level].slice == NULL);
 
-   mt->level[level].x_offset = malloc(nr_images * sizeof(GLuint));
-   mt->level[level].x_offset[0] = mt->level[level].level_x;
-   mt->level[level].y_offset = malloc(nr_images * sizeof(GLuint));
-   mt->level[level].y_offset[0] = mt->level[level].level_y;
+   mt->level[level].slice = malloc(nr_images * sizeof(*mt->level[0].slice));
+   mt->level[level].slice[0].x_offset = mt->level[level].level_x;
+   mt->level[level].slice[0].y_offset = mt->level[level].level_y;
 }
 
 
@@ -322,12 +320,13 @@ intel_miptree_set_image_offset(struct intel_mipmap_tree *mt,
 
    assert(img < mt->level[level].nr_images);
 
-   mt->level[level].x_offset[img] = mt->level[level].level_x + x;
-   mt->level[level].y_offset[img] = mt->level[level].level_y + y;
+   mt->level[level].slice[img].x_offset = mt->level[level].level_x + x;
+   mt->level[level].slice[img].y_offset = mt->level[level].level_y + y;
 
    DBG("%s level %d img %d pos %d,%d\n",
        __FUNCTION__, level, img,
-       mt->level[level].x_offset[img], mt->level[level].y_offset[img]);
+       mt->level[level].slice[img].x_offset,
+       mt->level[level].slice[img].y_offset);
 }
 
 
@@ -338,19 +337,19 @@ intel_miptree_get_image_offset(struct intel_mipmap_tree *mt,
 {
    switch (mt->target) {
    case GL_TEXTURE_CUBE_MAP_ARB:
-      *x = mt->level[level].x_offset[face];
-      *y = mt->level[level].y_offset[face];
+      *x = mt->level[level].slice[face].x_offset;
+      *y = mt->level[level].slice[face].y_offset;
       break;
    case GL_TEXTURE_3D:
    case GL_TEXTURE_2D_ARRAY_EXT:
    case GL_TEXTURE_1D_ARRAY_EXT:
       assert(depth < mt->level[level].nr_images);
-      *x = mt->level[level].x_offset[depth];
-      *y = mt->level[level].y_offset[depth];
+      *x = mt->level[level].slice[depth].x_offset;
+      *y = mt->level[level].slice[depth].y_offset;
       break;
    default:
-      *x = mt->level[level].x_offset[0];
-      *y = mt->level[level].y_offset[0];
+      *x = mt->level[level].slice[0].x_offset;
+      *y = mt->level[level].slice[0].y_offset;
       break;
    }
 }

src/mesa/drivers/dri/intel/intel_mipmap_tree.h

@@ -74,17 +74,30 @@ struct intel_mipmap_level
    /** Number of images at this level: 1 for 1D/2D, 6 for CUBE, depth for 3D */
    GLuint nr_images;
 
-   /** @{
-    * offsets from level_[xy] to the image for each cube face or depth
-    * level.
+   /**
+    * \brief List of 2D images in this mipmap level.
     *
-    * Pretty much have to accept that hardware formats
-    * are going to be so diverse that there is no unified way to
-    * compute the offsets of depth/cube images within a mipmap level,
-    * so have to store them as a lookup table.
+    * This may be a list of cube faces, array slices in 2D array texture, or
+    * layers in a 3D texture. The list's length is \c nr_images.
     */
-   GLuint *x_offset, *y_offset;
-   /** @} */
+   struct intel_mipmap_slice {
+      /**
+       * \name Offset to slice
+       * \{
+       *
+       * Hardware formats are so diverse that that there is no unified way to
+       * compute the slice offsets, so we store them in this table.
+       *
+       * The (x, y) offset to slice \c s at level \c l relative the miptrees
+       * base address is
+       * \code
+       *     x = mt->level[l].slice[s].x_offset
+       *     y = mt->level[l].slice[s].y_offset
+       */
+      GLuint x_offset;
+      GLuint y_offset;
+      /** \} */
+   } *slice;
 };
 
 struct intel_mipmap_tree