OK. to do something like XOR drawing...

dotted

Or Green Screen It seems like one needs a texture of the source elements and then a shader to perform the blending, yes?

Say I have two line2D and I want to have any overlap XORed (or another effect when a uv coordinate has non Color(0,0,0,0) in both textures.

CanvasItemMaterial is needed to hold the shader, blend mod of the material is irrelevant but the shader needs source textures to composite with.

cybereality

You can access textures in a shader by using uniform samplers.

uniform sampler2D other_texture;

Then you can get the texture using various functions (depends on what kind of node you are using) and then send that to the shader with set_shader_param().

dotted

@cybereality said: You can access textures in a shader by using uniform samplers.

Writing up a shader isn't an issue, it's all the other extraneous hoops to shift what i want to render to stuff them into textures in order to deploy a variant of splat mapping.

I think i have to:

construct yet another scene/set of nodes to contain what i want to render including a viewport and probably a camera or whatever
render an image to a texture (Viewport or whatever)
set up the shader to do its stuff
blah blah

All this to be able to create effects between rendered images, not bitmaps.

i understand that 99% of 2d is a bunch of bitmaps so this is a natural setup, but I'm rendering shapes in real time and have a mode that is closer to 3d where one works more with meshes and one performs effects on them.

at this point i really wish godot had taken a much more 3d-sh sensibility to its 2d polygon rendering pipeline

cybereality

With a Canvas Item Material, you can access the SCREEN_TEXTURE, which is basically the back buffer. This will allow you to composite 1 element over the screen, without using Viewports or any containers. In 3D, you can use the Render Priority to create layers (like in Photoshop) which will allow multiple objects to be composited. However, it does not appear that Render Priority exists in 2D, but maybe look into that. I may have missed something.

dotted

OK, this helps, I think.

Question: is the screen texture per canvas layer or for the 'screen' screen?

cybereality

It's the base screen. I know you can use Viewports for layering, but they can be expensive, you probably don't want more than 2 or 3 Viewports. But you can multiple textures to a shader and composite them in code.

dotted

@cybereality said: It's the base screen. I know you can use Viewports for layering, but they can be expensive, you probably don't want more than 2 or 3 Viewports. But you can multiple textures to a shader and composite them in code.

I am really tempted to consider exposing line-builder which underpins Line2D rendering. It generates the vertices

https://github.com/godotengine/godot/blob/master/scene/2d/line_2d.cpp

@ line 267 - 307

In any case, I may want to grab the mesh or render to a texture for other purposes, such as making small image to put into a particle effect.