98 lines
2.3 KiB
Go
98 lines
2.3 KiB
Go
package screen
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import (
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"image"
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"image/color"
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)
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const (
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shrWidth = 640
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shrWidthBytes = 640 / 4
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shrHeight = 200
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palettesCount = 256
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shrScanLineControlOffset = uint16(0x7d00)
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shrColorPalettesOffset = uint16(0x7e00)
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)
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func snapshotSuperHiRes(vs VideoSource) *image.RGBA {
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data := vs.GetSuperVideoMemory()
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return renderSuperHiRes(data)
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}
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func renderSuperHiRes(data []uint8) *image.RGBA {
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// See "Apple IIGS Hardware Reference", chapter 4, page 91
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// http://www.applelogic.org/files/GSHARDWAREREF.pdf
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size := image.Rect(0, 0, shrWidth, shrHeight)
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img := image.NewRGBA(size)
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// Load the palettes
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colors := make([]color.Color, palettesCount)
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iMem := uint16(0)
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for i := 0; i < palettesCount; i++ {
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b0 := data[iMem+shrColorPalettesOffset]
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iMem++
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b1 := data[iMem+shrColorPalettesOffset]
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iMem++
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red := (b1 & 0x0f) << 4
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green := b0 & 0xf0
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blue := (b0 & 0x0f) << 4
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colors[i] = color.RGBA{red, green, blue, 255}
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}
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// See "Apple IIGS Hardware Reference", table 4-21
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palettesSelectionTable := []uint8{0x4, 0x0, 0xc, 0x8}
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// Build the lines
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for y := 0; y < shrHeight; y++ {
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controlByte := data[uint16(y)+shrScanLineControlOffset]
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is640Wide := (controlByte & 0x80) != 0
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isColorFill := (controlByte & 0x20) != 0
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paletteIndex := (controlByte & 0x0f) << 4
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lineAddress := uint16(shrWidthBytes * y)
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lineBytes := data[lineAddress : lineAddress+shrWidthBytes]
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if is640Wide {
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// Line is 640 pixels, two bits per pixel
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x := 0
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for i := 0; i < shrWidthBytes; i++ {
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b := lineBytes[i]
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for j := 3; j >= 0; j-- {
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p := (b >> (uint(j) * 2)) & 0x03
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offset := palettesSelectionTable[j]
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color := colors[paletteIndex+offset+p]
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img.Set(x, y, color)
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x++
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}
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}
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} else {
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// Line is 320 pixels, two pixels per byte
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x := 0
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previousColor := uint8(0)
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for i := 0; i < shrWidthBytes; i++ {
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p0 := (lineBytes[i] & 0xf0) >> 4
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if isColorFill && p0 == 0 {
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p0 = previousColor
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} else {
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previousColor = p0
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}
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p1 := lineBytes[i] & 0x0f
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if isColorFill && p1 == 0 {
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p1 = previousColor
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} else {
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previousColor = p1
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}
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img.Set(x, y, colors[paletteIndex+p0])
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img.Set(x+1, y, colors[paletteIndex+p0])
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img.Set(x+2, y, colors[paletteIndex+p1])
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img.Set(x+3, y, colors[paletteIndex+p1])
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x += 4
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}
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}
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}
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return img
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}
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