80 lines
2.0 KiB
Go
80 lines
2.0 KiB
Go
package main
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import (
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"image"
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"image/color"
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"github.com/hajimehoshi/ebiten/v2"
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)
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const (
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GRAD_IDX_TOP = 0
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GRAD_IDX_BOTTOM = 1
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)
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func HexToRGBA(hexcolor int) color.RGBA {
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return color.RGBA{
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R: uint8(hexcolor >> 0x10 & 0xff),
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G: uint8(hexcolor >> 0x08 & 0xff),
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B: uint8(hexcolor >> 0x00 & 0xff),
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A: 0xff,
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}
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}
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type Gradient struct {
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Scene *ebiten.Image //our resultant image
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target *image.RGBA //raw pixel array
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width int
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height int
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colors []color.RGBA //gradient boundary colors
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}
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func NewGradient(width, height int) *Gradient {
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return &Gradient{
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Scene: ebiten.NewImage(width, height),
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target: image.NewRGBA(image.Rect(0, 0, width, height)),
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width: width,
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height: height,
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colors: []color.RGBA{HexToRGBA(0xFFFFFF), HexToRGBA(0x000000)},
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}
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}
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func (g *Gradient) SetColors(top, bottom color.RGBA) {
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g.colors[GRAD_IDX_TOP] = top
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g.colors[GRAD_IDX_BOTTOM] = bottom
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g.fillCurrent()
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}
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// performs linear fill on the currently set gradient values, top to bottom (0 to 1)
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func (g *Gradient) fill(top, bottom color.RGBA) {
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for y := 0; y < g.height; y++ {
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//the percent of our transition informs our blending
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percentIn := float64(y) / float64(g.height)
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//compute top and bottom blend values as factor of percentage
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pTopR := float64(top.R) * (1 - percentIn)
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pTopG := float64(top.G) * (1 - percentIn)
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pTopB := float64(top.B) * (1 - percentIn)
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pBottomR := float64(bottom.R) * (percentIn)
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pBottomG := float64(bottom.G) * (percentIn)
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pBottomB := float64(bottom.B) * (percentIn)
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//perform blending on per pixel row basis
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for x := 0; x < g.width; x++ {
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pixelIndex := 4 * (g.width*y + x)
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g.target.Pix[pixelIndex] = uint8(pTopR + pBottomR)
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g.target.Pix[pixelIndex+1] = uint8(pTopG + pBottomG)
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g.target.Pix[pixelIndex+2] = uint8(pTopB + pBottomB)
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g.target.Pix[pixelIndex+3] = 0xff
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}
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}
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g.Scene.WritePixels(g.target.Pix)
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}
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// gradient on currently set colors
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func (g *Gradient) fillCurrent() {
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g.fill(g.colors[GRAD_IDX_TOP], g.colors[GRAD_IDX_BOTTOM])
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}
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