cogl: Fix gl equivalent of blend string

An example of what could be the equivalent of
    "RBG = REPLACE(TEXTURE)
     A   = MODULATE(PREVIOUS,TEXTURE)"
using the ARB_texture_env_combine extension was given, but it seems that
a few typo were left:
    * remove a spurius GL_COMBINE_ALPHA
    * use the _ALPHA variant of SRCN and OPERANDN when setting up the
      alpha combiner

diff --git a/doc/reference/cogl/blend-strings.xml b/doc/reference/cogl/blend-strings.xml
index 9c3c8d3..0b37757 100644 (file)
--- a/doc/reference/cogl/blend-strings.xml
+++ b/doc/reference/cogl/blend-strings.xml
@@ -59,14 +59,13 @@ to this OpenGL code:
 <programlisting>
   glTexEnvi (GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE);
   glTexEnvi (GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_REPLACE);
-  glTexEnvi (GL_TEXTURE_ENV, GL_COMBINE_ALPHA, GL_REPLACE);
   glTexEnvi (GL_TEXTURE_ENV, GL_SRC0_RGB, GL_PREVIOUS);
   glTexEnvi (GL_TEXTURE_ENV, GL_OPERAND0_RGB, GL_SRC_COLOR);
   glTexEnvi (GL_TEXTURE_ENV, GL_COMBINE_ALPHA, GL_MODULATE);
-  glTexEnvi (GL_TEXTURE_ENV, GL_SRC0_RGB, GL_PREVIOUS);
-  glTexEnvi (GL_TEXTURE_ENV, GL_OPERAND0_RGB, GL_SRC_COLOR);
-  glTexEnvi (GL_TEXTURE_ENV, GL_SRC1_RGB, GL_TEXTURE);
-  glTexEnvi (GL_TEXTURE_ENV, GL_OPERAND1_RGB, GL_SRC_COLOR);
+  glTexEnvi (GL_TEXTURE_ENV, GL_SRC0_ALPHA, GL_PREVIOUS);
+  glTexEnvi (GL_TEXTURE_ENV, GL_OPERAND0_ALPHA, GL_SRC_COLOR);
+  glTexEnvi (GL_TEXTURE_ENV, GL_SRC1_ALPHA, GL_TEXTURE);
+  glTexEnvi (GL_TEXTURE_ENV, GL_OPERAND1_ALPHA, GL_SRC_COLOR);
 </programlisting>
 
 </section>