How to enable POINT_COORD in fragment shader for textured point sprites?

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:information_source: Attention Topic was automatically imported from the old Question2Answer platform.
:bust_in_silhouette: Asked By Skyfish
:warning: Old Version Published before Godot 3 was released.

Hello I want to draw some 3D Starfield in Godot. I’m fairly new to Godot and Shaders.

I use an ImmediateGeometry with attached skript (just test Data):

extends ImmediateGeometry

func _ready():
	self.begin(Mesh.PRIMITIVE_POINTS,null)
	for i in range(0, 3000):
		var x = rand_range(-1,1)
		var y = rand_range(-1,1)
		var z = rand_range(-0.2,0.2)
		self.add_vertex(Vector3(x,y,z))
	self.end()

I already managed to get the vertex shader to set the POINT_SIZE and COLOR in relation to the distance from camera.

uniform vec3 CameraPosition;
uniform float CameraZoom;
vec4 invcamx = INV_CAMERA_MATRIX.x;
vec4 invcamy = INV_CAMERA_MATRIX.y;
vec4 invcamz = INV_CAMERA_MATRIX.z;
vec4 invcamw = INV_CAMERA_MATRIX.w;
mat3 invcam = mat3(invcamx.xyz, invcamy.xyz, invcamz.xyz);
vec3 world_pos = (VERTEX - invcamw.xyz) * invcam;
float cameraDist = distance(CameraPosition.xyz,world_pos.xyz);
vec3 falloff = log(vec3(3-cameraDist,3-cameraDist,3-cameraDist));
COLOR = vec4(falloff.x, falloff.y , falloff.z,1);
POINT_SIZE = falloff.x * 32;

What I don’t get to work is the POINT_COORD in the Fragment shader. No Matter what I tried, I always get single colored point sprites instead of textured or multicolored ones when using POINT_COORD eg.:

DIFFUSE = vec3(POINT_COORD.x, POINT_COORD.y, 1);

I read that you need to gl.glEnable( 0x8861 ) in order to get gl_PointCoord to work like in this example:

http://badlogicgames.com/forum/viewtopic.php?t=658&p=3859

If you think POINT_COORD is not working, maybe you could submit a bug report with an example project showing it: Issues · godotengine/godot · GitHub

You could use world_pos or VERTEX in the meantime?

Zylann | 2017-02-15 18:18

POINT_COORD works for me at least, both when using ImmediateGeometry and points generated with SurfaceTool. Godot version is 2.1.1.stable.official. The fragment shader I’m using is:

uniform texture point_texture;

DIFFUSE_ALPHA = tex(point_texture, POINT_COORD);

mollusca | 2017-02-15 22:37

Are you using this in a fragment shader or a vertex shader?

Zylann | 2017-02-15 23:00

Ok thanks for the confirmation that it should work. But exactly this does not work in my fragment shader. I come to believe its a hardware problem? I use a lenovo ultrabook with NVIDIA Quadro. I will try this on my desktop when I’m home again and tell you the result.

Skyfish | 2017-02-16 07:47

On my desktop NVIDIA GTX 760 it’s even worse: even POINT_SIZE isn’t working which did work on my laptop. Nothing but dots instead of squares.

Skyfish | 2017-02-16 18:26

I opened an issue like you suggested: Point Sprites: POINT_SIZE / POINT_COORD not working in shader · Issue #7824 · godotengine/godot · GitHub

Skyfish | 2017-02-16 19:05

Note that POINT_SIZE is only accessible in vertex shaders, and POINT_COORD only available in fragment shaders.

http://docs.godotengine.org/en/stable/reference/shading_language.html?highlight=POINT_SIZE

Zylann | 2017-02-16 19:45