izapple2/screen/superHiRes.go
2020-10-17 13:31:42 +02:00

98 lines
2.3 KiB
Go

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