package apple2 import ( "image" "image/color" ) const ( shrWidth = 640 shrWidthBytes = 640 / 4 shrHeight = 200 palettesCount = 256 shrPixelDataAddress = uint16(0x2000) shrScanLineControlAddress = uint16(0x9d00) shrColorPalettesAddress = uint16(0x9e00) shrColorPalettesAddressEnd = uint16(0xa000) ) func snapshotSuperHiResMode(a *Apple2) *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 palletes palleteMem := a.mmu.physicalMainRAMAlt.subRange(shrColorPalettesAddress, shrColorPalettesAddressEnd) colors := make([]color.Color, palettesCount) iMem := 0 for i := 0; i < palettesCount; i++ { b0 := palleteMem[iMem] iMem++ b1 := palleteMem[iMem] 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 := a.mmu.physicalMainRAMAlt.peek(shrScanLineControlAddress + uint16(y)) is640Wide := (controlByte & 0x80) != 0 isColorFill := (controlByte & 0x20) != 0 palleteIndex := (controlByte & 0x0f) << 4 lineAddress := shrPixelDataAddress + uint16(shrWidthBytes*y) lineBytes := a.mmu.physicalMainRAMAlt.subRange(lineAddress, uint16(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[palleteIndex+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[palleteIndex+p0]) img.Set(x+1, y, colors[palleteIndex+p0]) img.Set(x+2, y, colors[palleteIndex+p1]) img.Set(x+3, y, colors[palleteIndex+p1]) x += 4 } } } return img }