From 362081ff6ef1bc91b0e880cedf176133069bfd98 Mon Sep 17 00:00:00 2001
From: Ivan Izaguirre <ivanizag@gmail.com>
Date: Fri, 3 May 2019 18:19:57 +0200
Subject: [PATCH] Initial NTSC emulation. Color as a filter on top of
 monochrome with half pixels

---
 apple2/screen.go | 74 ++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 72 insertions(+), 2 deletions(-)

diff --git a/apple2/screen.go b/apple2/screen.go
index c922d8f..d26f488 100644
--- a/apple2/screen.go
+++ b/apple2/screen.go
@@ -32,7 +32,9 @@ func Snapshot(a *Apple2) *image.RGBA {
 	} else {
 		if isHiResMode {
 			//return snapshotHiResModeReferenceMono(a, pageIndex)
-			return linesSeparatedFilter(snapshotHiResModeMonoShift(a, pageIndex))
+			//return linesSeparatedFilter(snapshotHiResModeMonoShift(a, pageIndex))
+			return linesSeparatedFilter(filterNTSCColor(snapshotHiResModeMonoShift(a, pageIndex)))
+
 			//return snapshotHiResModeReferenceColor(a, pageIndex)
 			//return snapshotHiResModeReferenceColorSolid(a, pageIndex)
 		} else {
@@ -78,6 +80,74 @@ func linesSeparatedFilter(in *image.RGBA) *image.RGBA {
 	return out
 }
 
+func filterNTSCColor(in *image.RGBA) *image.RGBA {
+	// RGB values from https://mrob.com/pub/xapple2/colors.html
+	black := color.RGBA{0, 0, 0, 255} /*COLOR=0 */ /*  0   0    0*/
+
+	dkBlue := color.RGBA{96, 78, 189, 255} /*COLOR=2 */ /*  0  60   25*/
+	red := color.RGBA{227, 30, 96, 255}    /*COLOR=1 */ /* 90  60   25*/
+	brown := color.RGBA{96, 114, 3, 255}   /*COLOR=8 */ /*180  60   25*/
+	dkGreen := color.RGBA{0, 163, 96, 255} /*COLOR=4 */ /*270  60   25*/
+
+	grey := color.RGBA{156, 156, 156, 255}  /*COLOR=10*/ /*  0   0   50*/
+	purple := color.RGBA{255, 68, 253, 255} /*HCOLOR=2*/ /* 45 100   50*/
+	orange := color.RGBA{255, 106, 60, 255} /*HCOLOR=5*/ /*135 100   50*/
+	green := color.RGBA{20, 245, 60, 255}   /*HCOLOR=1*/ /*225 100   50*/
+	blue := color.RGBA{20, 207, 253, 255}   /*HCOLOR=6*/ /*315 100   50*/
+
+	//purple := color.RGBA{255, 68, 253, 255} /*COLOR=3 */ /* 45 100   50*/
+	//orange := color.RGBA{255, 106, 60, 255} /*COLOR=9 */ /*135 100   50*/
+	//green := color.RGBA{20, 245, 60, 255} /*COLOR=12*/ /*225 100   50*/
+	//blue := color.RGBA{20, 207, 253, 255} /*COLOR=6 */ /*315 100   50*/
+
+	ltBlue := color.RGBA{208, 195, 255, 255} /*COLOR=7 */ /*  0  60   75*/
+	pink := color.RGBA{255, 160, 208, 255}   /*COLOR=11*/ /* 90  60   75*/
+	yellow := color.RGBA{208, 221, 141, 255} /*COLOR=13*/ /*180  60   75*/
+	aqua := color.RGBA{114, 255, 208, 255}   /*COLOR=14*/ /*270  60   75*/
+
+	white := color.RGBA{255, 255, 255, 255} /*COLOR=15*/ /*  0   0  100*/
+
+	colorMap := []color.Color{
+		/* 0000 */ black,
+		/* 0001 */ brown,
+		/* 0010 */ dkGreen,
+		/* 0011 */ green,
+		/* 0100 */ dkBlue,
+		/* 0101 */ grey,
+		/* 0110 */ blue,
+		/* 0111 */ aqua,
+		/* 1000 */ red,
+		/* 1001 */ orange,
+		/* 1010 */ grey,
+		/* 1011 */ yellow,
+		/* 1100 */ purple,
+		/* 1101 */ pink,
+		/* 1110 */ ltBlue,
+		/* 1111 */ white,
+	}
+
+	b := in.Bounds()
+	size := image.Rect(0, 0, b.Dx()/4, b.Dy())
+	out := image.NewRGBA(size)
+	for y := b.Min.Y; y < b.Max.Y; y++ {
+		for x := b.Min.X; x < b.Max.X; x += 4 {
+			v := 0
+			for i := 0; i < 4; i++ {
+				cIn := in.At(x+i, y)
+				r, _, _, _ := cIn.RGBA()
+				v = v << 1
+				if r != 0 {
+					v++
+				}
+			}
+			cOut := colorMap[v]
+			out.Set(x/4, y, cOut)
+		}
+	}
+	return out
+
+}
+
 const (
 	charWidth         = 7
 	charHeight        = 8
@@ -206,7 +276,7 @@ func snapshotHiResModeMonoShift(a *Apple2, page int) *image.RGBA {
 		x := 0
 		previousColour := color.Black
 		for _, b := range bytes {
-			shifted := b>>7 != 1
+			shifted := b>>7 == 1
 			for j := uint(0); j < 7; j++ {
 				bit := (b >> j) & 1
 				colour := color.Black