Support for lores graphics, per specs, no artifcats

apple2/screen.go

@@ -21,7 +21,7 @@ func Snapshot(a *Apple2) *image.RGBA {
 	isTextMode := a.io.isSoftSwitchActive(ioFlagText)
 	isHiResMode := a.io.isSoftSwitchActive(ioFlagHiRes)
 	isMixMode := a.io.isSoftSwitchActive(ioFlagMixed)
-	// Todo: isMixMode
+
 	pageIndex := 0
 	if a.io.isSoftSwitchActive(ioFlagSecondPage) {
 		pageIndex = 1
@@ -44,8 +44,9 @@ func Snapshot(a *Apple2) *image.RGBA {
 		if isHiResMode {
 			snap = snapshotHiResModeMonoShift(a, pageIndex, isMixMode, lightColor)
 		} else {
-			// Lo res mode not supported
-			return nil
+			snap = snapshotLoResModeReferenceColor(a, pageIndex, isMixMode)
+			isColor = false
+			isMixMode = false
 		}
 		if isMixMode {
 			snapText := snapshotTextMode(a, pageIndex, isHiResMode, lightColor)

apple2/screenHiRes.go

@@ -6,14 +6,14 @@ import (
 )
 
 const (
-	graphWidth        = 280
-	graphHeight       = 192
-	graphHeightMixed  = 160
-	graphPage1Address = uint16(0x2000)
-	graphPage2Address = uint16(0x4000)
+	hiResWidth        = 280
+	hiResHeight       = 192
+	hiResHeightMixed  = 160
+	hiResPage1Address = uint16(0x2000)
+	hiResPage2Address = uint16(0x4000)
 )
 
-func getGraphLineOffset(line int) uint16 {
+func getHiResLineOffset(line int) uint16 {
 
 	// See "Understanding the Apple II", page 5-14
 	// http://www.applelogic.org/files/UNDERSTANDINGTHEAII.pdf
@@ -23,13 +23,13 @@ func getGraphLineOffset(line int) uint16 {
 	return uint16(section*40 + outerEigth*0x80 + innerEigth*0x400)
 }
 
-func getGraphLine(a *Apple2, line int, page int) []uint8 {
-	address := graphPage1Address
+func getHiResLine(a *Apple2, line int, page int) []uint8 {
+	address := hiResPage1Address
 	if page == 1 {
-		address = graphPage2Address
+		address = hiResPage2Address
 	}
 
-	address += getGraphLineOffset(line)
+	address += getHiResLineOffset(line)
 	hi := uint8(address >> 8)
 	lo := uint8(address)
 
@@ -40,16 +40,16 @@ func getGraphLine(a *Apple2, line int, page int) []uint8 {
 func snapshotHiResModeMonoShift(a *Apple2, page int, mixedMode bool, light color.Color) *image.RGBA {
 	// As described in "Undertanding the Apple II", with half pixel shifts
 
-	height := graphHeight
+	height := hiResHeight
 	if mixedMode {
-		height = graphHeightMixed
+		height = hiResHeightMixed
 	}
 
-	size := image.Rect(0, 0, 2*graphWidth, height)
+	size := image.Rect(0, 0, 2*hiResWidth, height)
 	img := image.NewRGBA(size)
 
 	for y := 0; y < height; y++ {
-		bytes := getGraphLine(a, y, page)
+		bytes := getHiResLine(a, y, page)
 		x := 0
 		var previousColour color.Color = color.Black
 		for _, b := range bytes {
@@ -78,12 +78,12 @@ func snapshotHiResModeMonoShift(a *Apple2, page int, mixedMode bool, light color
 func snapshotHiResModeReferenceColor(a *Apple2, page int, mixedMode bool) *image.RGBA {
 	// As defined on "Apple II Reference Manual", page 19
 
-	height := graphHeight
+	height := hiResHeight
 	if mixedMode {
-		height = graphHeightMixed
+		height = hiResHeightMixed
 	}
 
-	size := image.Rect(0, 0, graphWidth, height)
+	size := image.Rect(0, 0, hiResWidth, height)
 	img := image.NewRGBA(size)
 
 	// RGB values from https://mrob.com/pub/xapple2/colors.html
@@ -109,7 +109,7 @@ func snapshotHiResModeReferenceColor(a *Apple2, page int, mixedMode bool) *image
 	}
 
 	for y := 0; y < height; y++ {
-		bytes := getGraphLine(a, y, page)
+		bytes := getHiResLine(a, y, page)
 		x := 0
 		previous := uint8(0)
 		for _, b := range bytes {
@@ -136,12 +136,12 @@ func snapshotHiResModeReferenceColorSolid(a *Apple2, page int, mixedMode bool) *
 	// As defined on "Apple II Reference Manual", page 19
 	// but with more solid colors and half the resolution
 
-	height := graphHeight
+	height := hiResHeight
 	if mixedMode {
-		height = graphHeightMixed
+		height = hiResHeightMixed
 	}
 
-	size := image.Rect(0, 0, graphWidth/2, height)
+	size := image.Rect(0, 0, hiResWidth/2, height)
 	img := image.NewRGBA(size)
 
 	// RGB values from https://mrob.com/pub/xapple2/colors.html
@@ -167,7 +167,7 @@ func snapshotHiResModeReferenceColorSolid(a *Apple2, page int, mixedMode bool) *
 	}
 
 	for y := 0; y < height; y++ {
-		bytes := getGraphLine(a, y, page)
+		bytes := getHiResLine(a, y, page)
 		x := 0
 		previous := uint8(0)
 		for _, b := range bytes {

apple2/screenHiRes_test.go

@@ -4,7 +4,7 @@ import (
 	"testing"
 )
 
-func TestGetGraphLineOffest(t *testing.T) {
+func TestGetHiResLineOffest(t *testing.T) {
 	scenarios := map[int]uint16{
 		0:   0x2000,
 		1:   0x2400,
@@ -16,7 +16,7 @@ func TestGetGraphLineOffest(t *testing.T) {
 	}
 
 	for in, want := range scenarios {
-		got := 0x2000 + getGraphLineOffset(in)
+		got := 0x2000 + getHiResLineOffset(in)
 		if want != got {
 			t.Errorf("expected %x but got %x for line %v", want, got, in)
 		}

apple2/screenLoRes.go

@@ -0,0 +1,119 @@
+package apple2
+
+import (
+	"image"
+)
+
+const (
+	loResPixelWidth  = charWidth
+	loResPixelHeight = charHeight / 2
+
+	loResWidth       = textColumns
+	loResHeight      = textLines * 2
+	loResHeightMixed = (textLines - textLinesMix) * 2
+	loRes
+	loResPage1Address = textPage1Address
+	loResPage2Address = textPage2Address
+)
+
+func snapshotLoResModeReferenceColor(a *Apple2, page int, mixedMode bool) *image.RGBA {
+	// As defined on "Apple II Reference Manual"
+
+	height := loResHeight
+	if mixedMode {
+		height = loResHeightMixed
+	}
+
+	size := image.Rect(0, 0, loResWidth, height)
+	img := image.NewRGBA(size)
+
+	// Lores colors correspond to the NTSC 4 bit patterns reversed
+	colorMap := getNTSCColorMap()
+	reversedNibble := []uint8{0, 8, 4, 12, 2, 10, 6, 14, 1, 9, 5, 13, 3, 11, 7, 15}
+
+	for y := 0; y < height; y = y + 2 {
+		for x := 0; x < loResWidth; x++ {
+			// Each text mode char encodes two pixels
+			char := getTextChar(a, x, y/2, page)
+			bottom := char >> 4
+			top := char & 0xf
+			img.Set(x, y, colorMap[reversedNibble[top]])
+			img.Set(x, y+1, colorMap[reversedNibble[bottom]])
+		}
+	}
+
+	return img
+}
+
+/*
+func getLoResLine(a *Apple2, line int, page int) []uint8 {
+	address := loResPage1Address
+	if page == 1 {
+		address = loResPage2Address
+	}
+
+	// Every text line encodes two lores lines
+	address += getTextCharOffset(0, line/2)
+	data := make([]uint8, 0, textColumns)
+	lower := (line % 2) == 1
+	for i := uint16(0); i < textColumns; i++ {
+		// Two pixels are encoded on each text page char position
+		v := a.mmu.internalPeek(address + i)
+		if lower {
+			// The four nost significant bits store the odd lines
+			v >>= 4
+		} else {
+			// The four least significant bits store the even lines
+			v &= 0xf
+		}
+		data = append(data)
+	}
+	return data
+}
+
+func snapshotLoResModeMonoShift(a *Apple2, page int, mixedMode bool, light color.Color) *image.RGBA {
+	// As described in "Undertanding the Apple II", with half pixel shifts
+
+	height := loResHeight
+	if mixedMode {
+		height = loResHeightMixed
+	}
+
+	size := image.Rect(0, 0, 2*loResWidth*loResPixelWidth, height*loResPixelHeight)
+	img := image.NewRGBA(size)
+
+	for y := 0; y < height; y++ {
+		bytes := getLoResLine(a, y, page)
+		x := 0
+		for i, v := range bytes {
+			// For each loRes 4bit pixel we have to complete 7*2 half mono pixels
+			for j := 0; j < 14; i++ {
+
+			}
+		}
+
+		x := 0
+		var previousColour color.Color = color.Black
+		for _, b := range bytes {
+			shifted := b>>7 == 1
+			for j := uint(0); j < 7; j++ {
+				bit := (b >> j) & 1
+				colour := light
+				if bit == 0 {
+					colour = color.Black
+				}
+
+				if shifted {
+					img.Set(x, y, previousColour)
+				} else {
+					img.Set(x, y, colour)
+				}
+				img.Set(x+1, y, colour)
+				previousColour = colour
+				x += 2
+			}
+		}
+	}
+	return img
+}
+*/

apple2/screenNtscFilter.go

@@ -50,6 +50,7 @@ func getNTSCColorMap() []color.Color {
 		/* 1110 */ ltBlue,
 		/* 1111 */ white,
 	}
+
 	return colorMap
 }