Ebiten: shader: Custom functions fail to compile

[nanoslayer]

Specifying custom functions would be a useful feature. For example:

func getColor(texCoord vec2) vec4 {
    color := texture0At(texCoord)
    // Do stuff with color
    return color
}

func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
    color := getColor(texCoord)
    // Do more stuff with color
    return color
}

[hajimehoshi]

I believe you can already do that.

[hajimehoshi]

func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
    color := getColor(texCoord)

This program shadows the argument color and is not valid (even as a regular Go program). I'll fix this to make a more friendly error message.

[nanoslayer]

I think I may have found a bug then. I was trying to implement linear filter and use a custom function at the same time. The shader would not compile, so I assumed that custom functions were not implemented.

Here is my shader code:

package main

func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
    texelSize := 1.0 / texture0Size()

    // Linear filter    
    p0 := texCoord - texelSize / 2.0
    p1 := texCoord + texelSize / 2.0

    c0 := getColor(p0)
    c1 := getColor(vec2(p1.x, p0.y))
    c2 := getColor(vec2(p0.x, p1.y))
    c3 := getColor(p1)

    rate := fract(p0 * texture0Size())
    return mix(mix(c0, c1, rate.x), mix(c2, c3, rate.x), rate.y)
}

func getColor(texCoord vec2) vec4 {
    // A simple example
    return texture0At(texCoord)
}

It gives the following error:

opengl: vertex shader compile error: opengl: shader compile failed: 0:21(2): error: no function with name 'F6'

[hajimehoshi]

Thanks. I'll take a look at this tonight.

[hajimehoshi]

Interesting. ~By optimization, a function definition was omitted. Hmm~ This seems a mysterious issue. F6 was actually defined but hidden?

[hajimehoshi]

My understanding is that function order matters like C. I'll add prototypes.

[nanoslayer]

That seems to have resolved the issue. Thank you!