wined3d: Map the destination BO with WINED3D_MAP_DISCARD when replacing the…

dlls/wined3d/context_gl.c

@@ -3062,6 +3062,7 @@ void wined3d_context_gl_copy_bo_address(struct wined3d_context_gl *context_gl,
         const struct wined3d_bo_address *dst, const struct wined3d_bo_address *src,
         unsigned int range_count, const struct wined3d_range *ranges)
 {
+    uint32_t map_flags = WINED3D_MAP_WRITE;
     const struct wined3d_gl_info *gl_info;
     struct wined3d_bo_gl *src_bo, *dst_bo;
     BYTE *dst_ptr, *src_ptr;
@@ -3071,6 +3072,9 @@ void wined3d_context_gl_copy_bo_address(struct wined3d_context_gl *context_gl,
     src_bo = src->buffer_object ? wined3d_bo_gl(src->buffer_object) : NULL;
     dst_bo = dst->buffer_object ? wined3d_bo_gl(dst->buffer_object) : NULL;
 
+    if (dst_bo && !dst->addr && !ranges->offset && ranges->size == dst_bo->size)
+        map_flags |= WINED3D_MAP_DISCARD;
+
     if (dst_bo && src_bo)
     {
         if (gl_info->supported[ARB_COPY_BUFFER])
@@ -3092,7 +3096,7 @@ void wined3d_context_gl_copy_bo_address(struct wined3d_context_gl *context_gl,
             src_ptr = wined3d_context_gl_map_bo_address(context_gl, src,
                     src_bo->size - (uintptr_t)src->addr, WINED3D_MAP_READ);
             dst_ptr = wined3d_context_gl_map_bo_address(context_gl, dst,
-                    dst_bo->size - (uintptr_t)dst->addr, WINED3D_MAP_WRITE);
+                    dst_bo->size - (uintptr_t)dst->addr, map_flags);
 
             for (i = 0; i < range_count; ++i)
                 memcpy(dst_ptr + ranges[i].offset, src_ptr + ranges[i].offset, ranges[i].size);