Lores mode using NTCS signal, showing artifacts

apple2/screen.go

@@ -44,12 +44,11 @@ func Snapshot(a *Apple2) *image.RGBA {
 		if isHiResMode {
 			snap = snapshotHiResModeMonoShift(a, pageIndex, isMixMode, lightColor)
 		} else {
-			snap = snapshotLoResModeReferenceColor(a, pageIndex, isMixMode)
-			isColor = false
-			isMixMode = false
+			snap = snapshotLoResModeMonoShift(a, pageIndex, isMixMode, lightColor)
 		}
+
 		if isMixMode {
-			snapText := snapshotTextMode(a, pageIndex, isHiResMode, lightColor)
+			snapText := snapshotTextMode(a, pageIndex, isMixMode, lightColor)
 			snap = mixSnapshots(snap, snapText)
 		}
 		if isColor {

apple2/screenLoRes.go

@@ -2,6 +2,7 @@ package apple2
 
 import (
 	"image"
+	"image/color"
 )
 
 const (
@@ -16,6 +17,17 @@ const (
 	loResPage2Address = textPage2Address
 )
 
+func getLoResPixel(a *Apple2, x int, y int, page int) uint8 {
+	// Each text mode char encodes two pixels
+	char := getTextChar(a, x, y/2, page)
+	if y%2 == 0 {
+		// Top pixel in char
+		return char & 0xf
+	}
+	// Bottom pixel in char
+	return char >> 4
+}
+
 func snapshotLoResModeReferenceColor(a *Apple2, page int, mixedMode bool) *image.RGBA {
 	// As defined on "Apple II Reference Manual"
 
@@ -31,44 +43,41 @@ func snapshotLoResModeReferenceColor(a *Apple2, page int, mixedMode bool) *image
 	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]])
+		for y := 0; y < height; y++ {
+			v := getLoResPixel(a, x, y, page)
+			img.Set(x, y, colorMap[reversedNibble[v]])
 		}
 	}
 
 	return img
 }
 
+func getColorPatterns(light color.Color) [16][16]color.Color {
 	/*
-func getLoResLine(a *Apple2, line int, page int) []uint8 {
-	address := loResPage1Address
-	if page == 1 {
-		address = loResPage2Address
-	}
+		For each lores pixel we have to fill 14 half mono pixels with
+		the 4 bits of the color repeated. We will need to shift by 2 bits
+		on the odd columns. Lets prepare 14+2 values for each color.
+	*/
 
-	// 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
+	var data [16][16]color.Color
+
+	for ci := 0; ci < 16; ci++ {
+		for cb := uint8(0); cb < 4; cb++ {
+			bit := (ci >> cb) & 1
+			var colour color.Color
+			if bit == 0 {
+				colour = color.Black
 			} else {
-			// The four least significant bits store the even lines
-			v &= 0xf
+				colour = light
+			}
+			for i := uint8(0); i < 4; i++ {
+				data[ci][cb+4*i] = colour
+			}
 		}
-		data = append(data)
 	}
 	return data
+
 }
 
 func snapshotLoResModeMonoShift(a *Apple2, page int, mixedMode bool, light color.Color) *image.RGBA {
@@ -82,38 +91,21 @@ func snapshotLoResModeMonoShift(a *Apple2, page int, mixedMode bool, light color
 	size := image.Rect(0, 0, 2*loResWidth*loResPixelWidth, height*loResPixelHeight)
 	img := image.NewRGBA(size)
 
+	patterns := getColorPatterns(light)
+
+	for x := 0; x < loResWidth; x++ {
 		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++ {
-
+			offset := (x % 2) * 2 // 2 pixel offset for odd lores pixels, 0 for even pixels
+			c := getLoResPixel(a, x, y, page)
+			// Insert the 14 half pixels required
+			for i := 0; i < loResPixelWidth*2; i++ {
+				v := patterns[c][i+offset]
+				// Repeat the same color for 4 lines
+				for r := 0; r < loResPixelHeight; r++ {
+					img.Set(x*loResPixelWidth*2+i, y*4+r, v)
 				}
 			}
-
-		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
 }
-*/