A Shader which simply flips whatever is above it on the Y axis without following the screen

Help Shaders
1

Godot Version

v4.2.2.stable.mono.official [15073afe3]

Question

To start off with it, I’m not very good with Shaders yet, I’m still learning, but I’m trying to figure out how to write a shader which I put on a Polygon2D, which should simply flip everything directly above it on the Y axis. This is what I got so far:

shader_type canvas_item;

uniform sampler2D screen : hint_screen_texture, filter_nearest;

void fragment() {
	vec4 ref = texture(screen, vec2(SCREEN_UV.x, 1.0 - SCREEN_UV.y + 0.3));
	COLOR = ref;
}

However, there’s one big issue with this. As I understand it, SCREEN_UV, as the name suggests, uses the viewport as reference. This causes the illusion to completely fall apart as soon as the camera moves up or down for any reason.

How can I modify this shader so it “ignores” the viewport moving up and down, and simply reflect CanvasItems?

2

you sure the node this shader applied to is following the camera?

3

The node this shader is attached to is not following the camera, that’s the whole point. This is attached to a simple Polygon2D which sits just under the player.

4

ok, i tested myself with movement up down, left right with camera on characterbody2d on water reflection shader. it kinda doesnt work only if i removed BackBufferCopy Node before the node with shader.

image

5

I’ll provide a bit more context to the post. I’m working on a 2D beat-em-up / platformer game, and this is supposed to be a somewhat simple but more flexible reflection method I can fine-tune. However, as it stands right now, it’s behavior is not correct, see the following example:

6

i suggest to check this video if you want a real working water reflection:

my code now has this line:

	float uv_height= SCREEN_PIXEL_SIZE.y/TEXTURE_PIXEL_SIZE.y;
	vec2 reflected_screen_uv = vec2(SCREEN_UV.x -(distortion*intensity*y_zoom*gradient.r), SCREEN_UV.y - uv_height * UV.y * y_zoom * scale.y * 2.0);

it actually calculate the uv_height, instead of just SCREEN_UV

which i see lacking from your code, hence results in weird behaviour when moving around

7

The video linked and the code provided does indeed seem to work with a Sprite2D, but does not work when using a Polygon2D, which is the main reason I needed a custom solution.

8

Using an empty AtlasTexture resource seem to do the trick, marking the last post as a solution.

9

well yes, i use texture masking so it can look any way i like instead of just rectangle shape

10

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