Rendering to offscreen buffer

[uzair jaleel]

Hello,

We are working on platform similar to linux and there is requirement where we want to render all composited content to an offscreen buffer like texture and

then draw that texture content onto a platform window.

Our requirement is that a third party application creates platform window in application side and we need to render the composited(UI+web page content) contents on that window.

Please could you help us pointing out in chromium code if support for offscreen rendering all ready exist ?

We came across https://source.chromium.org/chromium/chromium/src/+/main:components/viz/service/display_embedder/gl_output_surface_offscreen.h;bpv=1;bpt=1 where entire composited(UI+web page content) contents

are rendered into offscreen framebuffer backed by texture. 

Please could you let us know is there some scenario which is currently using fbo in class GLOutputSurfaceOffscreen ?

Your inputs will help us proceed in right direction.

Thanks in Advance

[Sunny Sachanandani]

> Our requirement is that a third party application creates platform window in application side and we need to render the composited(UI+web page content) contents on that window.

When you say "application side" do you mean that the window is created in the browser process?  Or in the viz/gpu process?  You'll also need to figure out a way to put the offscreen fbo contents on to the window, if you haven't already.  The OS might impose restrictions on what you can do with a window in another process (e.g. with direct composition on Windows).

> We came across https://source.chromium.org/chromium/chromium/src/+/main:components/viz/service/display_embedder/gl_output_surface_offscreen.h;bpv=1;bpt=1 where entire composited(UI+web page content) contents

are rendered into offscreen framebuffer backed by texture. 

If you're targeting a recent version of Chromium, you need to look at SkiaOutputDeviceOffscreen instead since we've migrated to SkiaRenderer on most platforms.

> Please could you let us know is there some scenario which is currently using fbo in class GLOutputSurfaceOffscreen ?

SkiaOutputDeviceOffscreen is definitely used in tests e.g. via the SetCapabilitiesForTesting call here: https://source.chromium.org/chromium/chromium/src/+/main:cc/test/pixel_test.cc;l=311;drc=2fb38c80b2764a7e3aed064975d8bdfdab961783;bpv=1;bpt=1?q=SkiaOutputDeviceOffscreen&ss=chromium%2Fchromium%2Fsrc

Others might know if we're using it in another non-testing scenario.

[uzair jaleel]

Hello Sunny,

Thanks for replying.

>When you say "application side" do you mean that the window is created in the browser process?  Or in the viz/gpu process? 

Window is created in browser process.

> You'll also need to figure out a way to put the offscreen fbo contents on to the window, if you haven't already.  The OS might impose restrictions on what you can do with a window in another process (e.g. with direct composition on Windows).

Is there any related code in chromium which draws the contents of offscreen fbo on window ?