I believe this falls out of section 4.4.5 Framebuffer Completeness.
"The internal formats of the attached images can affect the completeness of the framebuffer, so it is useful to first define the relationship between the internal format of an image and the attachment points to which it can be attached. Image internal formats are summarized in table 4.5. Color-renderable formats contain red, green, blue, and possibly alpha components; depth-renderable formats contain depth components; and stencil-renderable formats contain stencil components.
Formats not listed in table 4.5, including compressed internal formats. are not color-, depth-, or stencil-renderable, no matter which components they contain."
Table 4.5 lists DEPTH_COMPONENT16, RGBA4, RGB5_A1, RGB565, and STENCIL_INDEX8.
Even though the table legend says "renderbuffer image formats" the rest of the text leads me to believe this also applies to textures. Nowhere are LUMINANCE, LUMINANCE_ALPHA or ALPHA-only textures defined as color(?)-renderable.
Theoretically any extension which adds new renderbuffer or texture formats should augment this table and text if it wishes to define the formats to be renderable but many of the OES extensions are IMHO underspecified in this respect. (for example OES_rgb8_rgba8 -- what is the point in adding RGB8_OES and RGBA8_OES renderbuffers if you can't render to them?!)
Hope this helps,
On 2010-12-17, at 1:25 PM, Mo, Zhenyao wrote: