mesa/st: Add and use st_texture_image_transfer::box

Use this field to determine which parts of the compressed texture fallback
resource needs updating. Drops a dependency on the
st_texture_image_transfer::transfer pointer.

Acked-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18257>

src/mesa/state_tracker/st_cb_texture.c

@@ -507,6 +507,10 @@ st_MapTextureImage(struct gl_context *ctx,
          unsigned z = transfer->box.z;
          struct st_texture_image_transfer *itransfer = &texImage->transfer[z];
 
+         assert(itransfer->box.depth == 0);
+         if (transfer_flags & PIPE_MAP_WRITE)
+            u_box_2d_zslice(x, y, z, w, h, &itransfer->box);
+
          unsigned blk_w, blk_h;
          _mesa_get_format_block_size(texImage->TexFormat, &blk_w, &blk_h);
 
@@ -551,7 +555,9 @@ st_UnmapTextureImage(struct gl_context *ctx,
 
       assert(z == transfer->box.z);
 
-      if (transfer->usage & PIPE_MAP_WRITE) {
+      if (itransfer->box.depth != 0) {
+         assert(itransfer->box.depth == 1);
+
          if (util_format_is_compressed(texImage->pt->format)) {
             /* Transcode into a different compressed format. */
             unsigned size =
@@ -631,6 +637,8 @@ st_UnmapTextureImage(struct gl_context *ctx,
                unreachable("unexpected format for a compressed format fallback");
             }
          }
+
+         memset(&itransfer->box, 0, sizeof(struct pipe_box));
       }
 
       itransfer->temp_data = NULL;

src/mesa/state_tracker/st_texture.h

@@ -47,6 +47,7 @@ struct st_texture_image_transfer
    GLubyte *temp_data; /**< Temporary compressed texture storage. */
    unsigned temp_stride; /**< Stride of the compressed texture storage. */
    GLubyte *map; /**< Saved map pointer of the uncompressed transfer. */
+   struct pipe_box box; /**< Region of the transfer's resource to write. */
 };