mesa: new _mesa_prepare_mipmap_level() function for mipmap generation

This helper function is used during mipmap generation to prepare space
for the destination mipmap levels.

This improves/fixes two things:
1. If the texture object was created with glTexStorage2D, calling
   _mesa_TexImage2D() to allocate the new image would generate
   INVALID_OPERATION since the texture is marked as immutable.
2. _mesa_TexImage2D() always frees any existing texture image memory
   before allocating new memory.  That's inefficient if the existing
   image is the right size already.

Reviewed-by: Ian Romanick <[email protected]>
Reviewed-by: Eric Anholt <[email protected]>

1 files changed, 6 insertions, 0 deletions

diff --git a/src/mesa/main/mipmap.h b/src/mesa/main/mipmap.h
index 1fb9146a163..072794cb6ad 100644
--- a/src/mesa/main/mipmap.h
+++ b/src/mesa/main/mipmap.h
@@ -41,6 +41,12 @@ _mesa_generate_mipmap_level(GLenum target,
                             GLint dstRowStride);
 
 
+extern GLboolean
+_mesa_prepare_mipmap_level(struct gl_context *ctx,
+                           struct gl_texture_object *texObj, GLuint level,
+                           GLsizei width, GLsizei height, GLsizei depth,
+                           GLsizei border, GLenum intFormat, gl_format format);
+
 extern void
 _mesa_generate_mipmap(struct gl_context *ctx, GLenum target,
                       struct gl_texture_object *texObj);