Android: Dual Pass Render To SurfaceTexture Using OpenGL

Question

In order to perform a Gaussian blur on a SurfaceTexture, I am performing a dual pass render, meaning that I am passing the texture through one shader (horizontal blur) and then through another shader (vertical blur).

I understand the theory behind this: render the first texture to an FBO and the second one onto the SurfaceTexture itself.

There are some examples of this, but none of them seem applicable since a SurfaceTexture uses GL_TEXTURE_EXTERNAL_OES as its target in glBindTexture rather than GL_TEXTURE_2D. Therefore, in the call to glFramebufferTexture2D, GL_TEXTURE_2D cannot be used as the textarget, and I don't think GL_TEXTURE_EXTERNAL_OES can be used in this call.

Can anyone suggest a way to render a texture twice, with the final rendering going to a SurfaceTexture?

Important update: I am using a SurfaceTexture since this is a dynamic blur of a video that plays onto a surface.

Edit: This question was asked with some misunderstanding on my part. A SurfaceTexture is not a display element. It instead receives data from a surface, and is attached to a GL_TEXTURE_EXTERNAL_OES.

Thank you.

I have always used GL_TEXTURE_2D. Does this not work for you for some reason? — Matic Oblak
When I use GL_TEXTURE_EXTERNAL_OES as the target for glBindTexture, then I get an invalid operation error when passing the same texture name in glFramebufferTexture2D, regardless of whether I use GL_TEXTURE_2D or GL_TEXTURE_EXTERNAL_OES in that call. The binding seems to work if the target in glBindTexture is GL_TEXTURE_2D, but then obviously I can't render the FBO to a SurfaceTexture anymore. — Michael

fadden fadden · Accepted Answer · 2016-02-02T17:04:05

Rendering to a SurfaceTexture seems like an odd thing to do here. The point of SurfaceTexture is to take whatever is sent to the Surface and convert it into a GLES "external" texture. Since you're rendering with GLES, you can just use an FBO to render into a GL_TEXTURE_2D for your second pass.

SurfaceTexture is used when receiving frames from Camera or a video decoder because the source is usually YUV. The "external" texture format allows for a wider range of pixel formats, but constrains the uses of the texture. There's no value in rendering to a SurfaceTexture with GLES if your goal is to create a GLES texture.

Android: Dual Pass Render To SurfaceTexture Using OpenGL

1 Answers