cogl: Make CoglSubTexture only work for quad rendering

The sub texture backend doesn't work well as a completely general
texture backend because for example when rendering with cogl_polygon
it needs to be able to tranform arbitrary texture coordinates without
reference to the other coordintes. This can't be done when the texture
coordinates are a multiple of one because sometimes the coordinate
should represent the left or top edge and sometimes it should
represent the bottom or top edge. For example if the s coordinates are
0 and 1 then 1 represents the right edge but if they are 1 and 2 then
1 represents the left edge.

Instead the sub-textures are now documented not to support coordinates
outside the range [0,1]. The coordinates for the sub-region are now
represented as integers as this helps avoid rounding issues. The
region can no longer be a super-region of the texture as this
simplifies the code quite a lot.

There are two new texture virtual functions:

transform_quad_coords_to_gl - This transforms two pairs of coordinates
     representing a quad. It will return FALSE if the coordinates can
     not be transformed. The sub texture backend uses this to detect
     coordinates that require repeating which causes cogl-primitives
     to use manual repeating.

ensure_non_quad_rendering - This is used in cogl_polygon and
     cogl_vertex_buffer to inform the texture backend that
     transform_quad_to_gl is going to be used. The atlas backend
     migrates the texture out of the atlas when it hits this.

1 files changed, 7 insertions, 8 deletions

diff --git a/cogl/cogl-sub-texture-private.h b/cogl/cogl-sub-texture-private.h
index 899f61e8..c8fa4bbc 100644
--- a/cogl/cogl-sub-texture-private.h
+++ b/cogl/cogl-sub-texture-private.h
@@ -37,12 +37,11 @@ struct _CoglSubTexture
 
   CoglHandle  full_texture;
 
-  /* The texture coordinates of the subregion of full_texture */
-  gfloat      tx1, ty1;
-  gfloat      tx2, ty2;
-
-  /* Are all of the texture coordinates a multiple of one? */
-  gboolean    tex_coords_are_a_multiple;
+  /* The region represented by this sub-texture */
+  gint        sub_x;
+  gint        sub_y;
+  gint        sub_width;
+  gint        sub_height;
 };
 
 GQuark
@@ -50,7 +49,7 @@ _cogl_handle_sub_texture_get_type (void);
 
 CoglHandle
 _cogl_sub_texture_new (CoglHandle full_texture,
-                       gfloat tx1, gfloat ty1,
-                       gfloat tx2, gfloat ty2);
+                       gint sub_x, gint sub_y,
+                       gint sub_width, gint sub_height);
 
 #endif /* __COGL_SUB_TEXTURE_H */