vrend: fallback to GL_OES_EGL_image instead of GL_OES_EGL_image_external

Ryan Neph requested to merge ryanneph/virglrenderer:gl_oes_egl_image into master

Mesa implements GL_OES_EGL_image for OpenGL and GLES, while GL_OES_EGL_image_external is only implemented for GLES. Chrome OS requires GL_OES_EGL_image and GL_OES_EGL_image_external to be implemented by GL/GLES drivers, so requiring GL_OES_EGL_image is acceptable.

Also, the current usage of glEGLImageTargetTexture2DOES() matches that specified by GL_OES_EGL_image rather than GL_OES_EGL_image_external (target is GL_TEXTURE_2D rather than GL_TEXTURE_EXTERNAL_OES). More work is needed if we want to support GL_OES_EGL_image_external as well when GL_OES_EGL_image is not available.

Signed-off-by: Ryan Neph ryanneph@google.com

This addresses #275 (closed).

/cc @chadversary @zzyiwei

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