Crash when using modf in own shader

[Nophlock]

Godot version:
(3.0-Stable)

OS/device including version:
Windows 10
Radeon RX 570 with Radeon 18.1.1

Issue description:
Today I wanted to play around with the built in shaders and for that I wanted to use the modf command, but as soon as I typed in this line:

if( mod(UV.x,0.1) == 0.0)
{
ALBEDO = vec3(1.0,0.0,0.0);
}

It crashed immediatly and when I saved the shader before it got applied to the object, I couldn't reopen the project/scene until I manually edit the shader in the corresponding shaderfile to something else.

Steps to reproduce:
Create a new mesh, image or any type of objects that accept materials or own shaders. After that create a new "ShaderMaterial" for this object and open the builtin shaderedior. Type in a shader that is using modf or copy the following shader to the editor and wait until Godot wants to apply it:

shader_type spatial;
uniform float grid_size = 1.0;

void fragment()
{
if( modf(UV.x,0.1) == 0.0)
{
ALBEDO = vec3(1.0,0.0,0.0);
}
else
{
ALBEDO = vec3(0.0);
}
}

Note: Godot doesn't crash with the "mod"-Function, only with "modf" and I suggest you not to save the shader, except you want to edit the shaderfile all the time to reopen the project/scene ^^

Minimal reproduction project:
Please note that in this example project I used "mod" so Godot doesn't crash at the startup. Just replace "mod" with "modf" in the shader and you are "good to go".
ModfBug.zip

[hpvb]

I just tried this and Godot doesn't crash for me. I do get a shader compiler error though:

ERROR: _display_error_with_code: SceneShaderGLES3: Fragment Program Compilation Failed:
0:1166(25): error: function parameter 'out i' is not an lvalue
0:1166(7): error: operands of `==' must have the same type

   At: drivers/gles3/shader_gles3.cpp:168.
ERROR: get_current_version: SceneShaderGLES3: Fragment Program Compilation Failed:
0:1166(25): error: function parameter 'out i' is not an lvalue
0:1166(7): error: operands of `==' must have the same type

   At: drivers/gles3/shader_gles3.cpp:441.
ERROR: get_current_version: Method/Function Failed, returning: __null
   At: drivers/gles3/shader_gles3.cpp:449.
ERROR: bind: Condition ' !version ' is true. returned: false
   At: drivers/gles3/shader_gles3.cpp:123.
ERROR: _get_uniform: Condition ' !version ' is true. returned: -1
   At: drivers/gles3/shader_gles3.h:377.
ERROR: _get_uniform: Condition ' !version ' is true. returned: -1
   At: drivers/gles3/shader_gles3.h:377.
ERROR: _get_uniform: Condition ' !version ' is true. returned: -1
   At: drivers/gles3/shader_gles3.h:377.
ERROR: _get_uniform: Condition ' !version ' is true. returned: -1
   At: drivers/gles3/shader_gles3.h:377.
ERROR: _get_uniform: Condition ' !version ' is true. returned: -1
   At: drivers/gles3/shader_gles3.h:377.

[Nophlock]

@hpvb
Ok, I gave this a try on a Fedora system now and it doesn't crash there. Instead I get the same error message as you(so you probably tested it on Linux too? ^^), which shouldn't popup anyway or did I used modf wrong and this is related to an driver issue on my Windows machine?

[vnen]

I get the errors on Windows 10 x64 with a Radeon RX 480, but it doesn't crash. Are your drivers up-to-date?

[hpvb]

This shader probably shouldn't be submitted to the driver at all though. I'd still call that a bug, irrespective of the driver bug.

[Nophlock]

@vnen
Yeah I got the newest one or at least the Radeon driver tells me that I have the newest one which is 18.1.1

@hpvb
Alright

Topic:
I don't know if this helps but when I run Godot from the Cmd window to see what Godot is printing when it crashes, I get this:

[binbitten]

Second argument of modf() is actually an output parameter. Seems godot does not prevent using constants as outputs, which will cause glsl-error or crash depending on the driver.

[Nophlock]

@binbitten
Oh wow, totally overlooked the "out" parameter in the documentation, this explains a few things...

[Nophlock]

Just to give this a little update: I've managed to compile Godot from the sources and with that, enable the Backtrace which hopefully helps more than the old one ...

[Zylann]

Godot 3.0.5
Windows 10 64 bits
GeForce GTX 1060 6GB/PCIe/SSE2

I get broken rendering if I use this shader:

shader_type spatial;

uniform sampler2D u_noise;

void fragment() {
	float n = texture(u_noise, UV).r;
	n += modf(TIME, 1.0);
	EMISSION = vec3(n, n, n);
}

[vnen]

@Zylann as mentioned earlier, second argument of modfis an out parameter.