ebiten: add `FilterCrispScaling`

[hajimehoshi]

Operating System

• [ ] Windows
• [ ] macOS
• [ ] Linux
• [ ] FreeBSD
• [ ] OpenBSD
• [ ] Android
• [ ] iOS
• [ ] Nintendo Switch
• [ ] PlayStation 5
• [ ] Xbox
• [ ] Web Browsers

What feature would you like to be added?

We propose to add a new filter FilterCripsScaling, which enlarges the image without losing crisp edges and without being blurred. This is the same scaling as the current Ebitengine screen's scaling.

The current problem is that the filter might not work well when rotating.

In the future, we might be able to replace the default filter from FilterNearest, but we are not sure.

Why is this needed?

To provide a better scaling instead of FilterNearest.

[hajimehoshi]

Is there a way to do this without any uniform variables?

[hajimehoshi]

https://www.shadertoy.com/view/MlB3D3

[hajimehoshi]

This worked well:

//kage:unit pixels

package main

func Fragment(dstPos vec4, srcPos vec2, color vec4) vec4 {
    // Blend source colors in a rectangle region, whose size is inverseScale.
    inverseScale := vec2(abs(dfdx(srcPos.x)), abs(dfdy(srcPos.y)))
    pos := srcPos
    p0 := pos - inverseScale/2.0
    p1 := pos + inverseScale/2.0

    c0 := imageSrc0UnsafeAt(p0)
    c1 := imageSrc0UnsafeAt(vec2(p1.x, p0.y))
    c2 := imageSrc0UnsafeAt(vec2(p0.x, p1.y))
    c3 := imageSrc0UnsafeAt(p1)

    rate := clamp(fract(p1)/inverseScale, 0, 1)
    return mix(mix(c0, c1, rate.x), mix(c2, c3, rate.x), rate.y) * color
}