i965: Document conventions for counting layers in 2D multisample buffers.

The "layer" parameters used in blorp, and the
intel_renderbuffer::mt_layer field, represent a physical layer rather
than a logical layer.  This is important for 2D multisample arrays on
Gen7+ because the UMS and CMS multisample layouts use N physical
layers to represent each logical layer, where N is the number of
samples.

Also add an assertion to blorp to help catch bugs if we fail to follow
these conventions.

Reviewed-by: Chad Versace <chad.versace@linux.intel.com>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/i965/brw_blorp.cpp

@@ -54,6 +54,15 @@ void
 brw_blorp_mip_info::set(struct intel_mipmap_tree *mt,
                         unsigned int level, unsigned int layer)
 {
+   /* Layer is a physical layer, so if this is a 2D multisample array texture
+    * using INTEL_MSAA_LAYOUT_UMS or INTEL_MSAA_LAYOUT_CMS, then it had better
+    * be a multiple of num_samples.
+    */
+   if (mt->msaa_layout == INTEL_MSAA_LAYOUT_UMS ||
+       mt->msaa_layout == INTEL_MSAA_LAYOUT_CMS) {
+      assert(layer % mt->num_samples == 0);
+   }
+
    intel_miptree_check_level_layer(mt, level, layer);
 
    this->mt = mt;

src/mesa/drivers/dri/i965/brw_blorp.h

@@ -85,6 +85,11 @@ public:
    /**
     * The 2D layer within the miplevel. Combined, level and layer define the
     * 2D miptree slice to use.
+    *
+    * Note: if mt is a 2D multisample array texture on Gen7+ using
+    * INTEL_MSAA_LAYOUT_UMS or INTEL_MSAA_LAYOUT_CMS, layer is the physical
+    * layer holding sample 0.  So, for example, if mt->num_samples == 4, then
+    * logical layer n corresponds to layer == 4*n.
     */
    uint32_t layer;
 

src/mesa/drivers/dri/i965/brw_blorp_blit.cpp

@@ -123,6 +123,14 @@ find_miptree(GLbitfield buffer_bit, struct intel_renderbuffer *irb)
    return mt;
 }
 
+
+/**
+ * Note: if the src (or dst) is a 2D multisample array texture on Gen7+ using
+ * INTEL_MSAA_LAYOUT_UMS or INTEL_MSAA_LAYOUT_CMS, src_layer (dst_layer) is
+ * the physical layer holding sample 0.  So, for example, if
+ * src_mt->num_samples == 4, then logical layer n corresponds to src_layer ==
+ * 4*n.
+ */
 void
 brw_blorp_blit_miptrees(struct brw_context *brw,
                         struct intel_mipmap_tree *src_mt,

src/mesa/drivers/dri/i965/intel_fbo.h

@@ -63,6 +63,11 @@ struct intel_renderbuffer
     *
     * For renderbuffers not created with glFramebufferTexture*(), mt_level and
     * mt_layer are 0.
+    *
+    * Note: for a 2D multisample array texture on Gen7+ using
+    * INTEL_MSAA_LAYOUT_UMS or INTEL_MSAA_LAYOUT_CMS, mt_layer is the physical
+    * layer holding sample 0.  So, for example, if mt->num_samples == 4, then
+    * logical layer n corresponds to mt_layer == 4*n.
     */
    unsigned int mt_level;
    unsigned int mt_layer;