How can one write to multiple textures from a fragment shader (a la opengl's COLOR_ATTACHMENT's)?

[Qix-]

For a single view, I'd like to write to multiple textures that are assigned to its frame buffer via setViewFrameBuffer().

Right now there's just a single texture attached to a frame buffer and set as that view's frame buffer, which I use the typical gl_FragColor output variable to write to.

Is there a way to set the color of a second texture? I see that multiple textures can be provided when calling createFrameBuffer() but it's not clear from the examples how to actually write to them via a fragment shader.

Any information is super helpful!

[bkaradzic]

See MRT example: https://bkaradzic.github.io/bgfx/examples.html#deferred

Writing into MRT:

bgfx/examples/21-deferred/fs_deferred_geom.sc

Lines 29 to 30 in c084dd2

	gl_FragData[0] = texture2D(s_texColor, v_texcoord0);
	gl_FragData[1] = vec4(encodeNormalUint(wnormal), 1.0);

[Qix-]

Aha! Thanks! So is gl_FragColor just an alias for gl_FragData[0] or something?

[bkaradzic]

Yes.

[Qix-]

Amazing, thanks @bkaradzic :)

[Qix-]

Hey sorry to pick this back up.

What about gl_FragDepth? If I'm setting the frame buffer, do I also need to attach a third texture that is a D8 or something in order to get that to work? If so, in which order should I include it? I'm writing depth information but blending still isn't working correctly and I suspect it's because I just have two RGBA8 textures in the frame buffer without anywhere for the depth information to be stored.

Or am I way off base?

[Qix-]

Nevermind, checked the deferred example again and indeed had missed the depth buffer. All is good!