Add support for RG textures

This adds COGL_PIXEL_FORMAT_RG_88 and COGL_TEXTURE_COMPONENTS_RG in
order to support two-component textures. The RG components for a
texture is only supported if COGL_FEATURE_ID_TEXTURE_RG is advertised.
This is only available on GL 3, GL 2 with the GL_ARB_texture_rg
extension or GLES with the GL_EXT_texture_rg extension. The RG pixel
format is always supported for images because Cogl can easily do the
conversion if an application uses this format to upload to a texture
with a different format.

If an application tries to create an RG texture when the feature isn't
supported then it will raise an error when the texture is allocated.

https://bugzilla.gnome.org/show_bug.cgi?id=712830

Reviewed-by: Robert Bragg <robert@linux.intel.com>

1 files changed, 31 insertions, 9 deletions

diff --git a/cogl/cogl-bitmap-conversion.c b/cogl/cogl-bitmap-conversion.c
index 6a2e8507..b6d9b149 100644
--- a/cogl/cogl-bitmap-conversion.c
+++ b/cogl/cogl-bitmap-conversion.c
@@ -325,6 +325,7 @@ _cogl_bitmap_needs_short_temp_buffer (CoglPixelFormat format)
       g_assert_not_reached ();
 
     case COGL_PIXEL_FORMAT_A_8:
+    case COGL_PIXEL_FORMAT_RG_88:
     case COGL_PIXEL_FORMAT_RGB_565:
     case COGL_PIXEL_FORMAT_RGBA_4444:
     case COGL_PIXEL_FORMAT_RGBA_5551:
@@ -512,6 +513,35 @@ _cogl_bitmap_convert (CoglBitmap *src_bmp,
   return dst_bmp;
 }
 
+static CoglBool
+driver_can_convert (CoglContext *ctx,
+                    CoglPixelFormat src_format,
+                    CoglPixelFormat internal_format)
+{
+  if (!_cogl_has_private_feature (ctx, COGL_PRIVATE_FEATURE_FORMAT_CONVERSION))
+    return FALSE;
+
+  if (src_format == internal_format)
+    return TRUE;
+
+  /* If the driver doesn't natively support alpha textures then it
+   * won't work correctly to convert to/from component-alpha
+   * textures */
+  if (!_cogl_has_private_feature (ctx, COGL_PRIVATE_FEATURE_ALPHA_TEXTURES) &&
+      (src_format == COGL_PIXEL_FORMAT_A_8 ||
+       internal_format == COGL_PIXEL_FORMAT_A_8))
+    return FALSE;
+
+  /* Same for red-green textures. If red-green textures aren't
+   * supported then the internal format should never be RG_88 but we
+   * should still be able to convert from an RG source image */
+  if (!cogl_has_feature (ctx, COGL_FEATURE_ID_TEXTURE_RG) &&
+      src_format == COGL_PIXEL_FORMAT_RG_88)
+    return FALSE;
+
+  return TRUE;
+}
+
 CoglBitmap *
 _cogl_bitmap_convert_for_upload (CoglBitmap *src_bmp,
                                  CoglPixelFormat internal_format,
@@ -532,15 +562,7 @@ _cogl_bitmap_convert_for_upload (CoglBitmap *src_bmp,
      limited number of formats so we must convert using the Cogl
      bitmap code instead */
 
-  /* If the driver doesn't natively support alpha textures then it
-   * won't work correctly to convert to/from component-alpha
-   * textures */
-
-  if (_cogl_has_private_feature (ctx, COGL_PRIVATE_FEATURE_FORMAT_CONVERSION) &&
-      (_cogl_has_private_feature (ctx, COGL_PRIVATE_FEATURE_ALPHA_TEXTURES) ||
-       (src_format != COGL_PIXEL_FORMAT_A_8 &&
-        internal_format != COGL_PIXEL_FORMAT_A_8) ||
-       src_format == internal_format))
+  if (driver_can_convert (ctx, src_format, internal_format))
     {
       /* If the source format does not have the same premult flag as the
          internal_format then we need to copy and convert it */