Save GIFs on headless mode

.gitignore

@@ -4,4 +4,7 @@ a2sdl.exe
 frontend/a2sdl/a2sdl
 frontend/a2sdl/*.woz
 frontend/a2sdl/*.dsk
-frontend/a2fyne/a2fyne
+frontend/a2fyne/a2fyne
+frontend/headless/headless
+frontend/*/snapshot.gif
+frontend/*/snapshot.png

frontend/headless/main.go

@@ -3,8 +3,10 @@ package main
 import (
 	"bufio"
 	"fmt"
+	"image/gif"
 	"os"
 	"strings"
+	"time"
 
 	"github.com/ivanizag/izapple2"
 	"github.com/ivanizag/izapple2/screen"
@@ -88,6 +90,9 @@ func main() {
 		case "return":
 			fe.keyChannel <- 13
 
+		case "gif":
+			SaveGif(a, "snapshot.gif")
+
 		case "help":
 			fmt.Print(`
 Available commands:
@@ -99,6 +104,7 @@ Available commands:
 	Key or k: Sends a key to the emulator
 	Keys or ks: Sends a string to the emulator
 	Return or r: Sends a return to the emulator
+	GIF or gif: Captures a GIF animation
 	Help: Prints this help
 `)
 		default:
@@ -107,6 +113,40 @@ Available commands:
 	}
 }
 
+func SaveGif(a *izapple2.Apple2, filename string) error {
+	animation := gif.GIF{}
+
+	delay := 50 * time.Millisecond
+	delayHundredsS := 5
+	frames := 20 // 1 second
+
+	planned := time.Now()
+	for i := 0; i < frames; i++ {
+		lapse := planned.Sub(time.Now())
+		fmt.Printf("%v\n", lapse)
+		if lapse > 0 {
+			time.Sleep(lapse)
+		}
+
+		fmt.Printf("%v\n", time.Now())
+		img := screen.SnapshotPaletted(a, screen.ScreenModeNTSC)
+		animation.Image = append(animation.Image, img)
+		animation.Delay = append(animation.Delay, delayHundredsS)
+
+		planned = planned.Add(delay)
+	}
+
+	f, err := os.Create(filename)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	gif.EncodeAll(f, &animation)
+	return nil
+
+}
+
 /*
 Uses the console to send commands and queries to an emulated machine.
 */

screen/ntscFilter.go

@@ -30,6 +30,21 @@ var ntscColorMap = [16]color.Color{
 	color.RGBA{255, 255, 255, 255}, // White
 }
 
+var attenuatedColorMap = buildAttenuatedColorMap(ntscColorMap)
+
+func buildAttenuatedColorMap(colorMap [16]color.Color) [16]color.Color {
+	colors := [16]color.Color{}
+	for i := 0; i < len(colorMap); i++ {
+		r, g, b, _ := colorMap[i].RGBA()
+		colors[i] = color.RGBA64{
+			uint16(r / 2), uint16(g / 2), uint16(b / 2),
+			65535,
+		}
+	}
+	return colors
+}
+
+/*
 var rgbColorMap = [16]color.Color{
 	color.RGBA{0, 0, 0, 255},       // Black
 	color.RGBA{221, 0, 51, 255},    // Magenta
@@ -48,18 +63,13 @@ var rgbColorMap = [16]color.Color{
 	color.RGBA{68, 255, 153, 255},  // Aquamarine
 	color.RGBA{255, 255, 255, 255}, // White
 }
+*/
 
 func filterNTSCColor(in *image.RGBA, mask *image.Alpha, screenMode int) *image.RGBA {
 	colorMap := ntscColorMap // or rgbColorMap
-	attenuatedColorMap := ntscColorMap
+	colorMapLow := ntscColorMap
 	if screenMode == ScreenModeNTSC {
-		for i := 0; i < len(colorMap); i++ {
-			r, g, b, _ := colorMap[i].RGBA()
-			attenuatedColorMap[i] = color.RGBA64{
-				uint16(r / 2), uint16(g / 2), uint16(b / 2),
-				65535,
-			}
-		}
+		colorMapLow = attenuatedColorMap
 	}
 
 	b := in.Bounds()
@@ -90,7 +100,7 @@ func filterNTSCColor(in *image.RGBA, mask *image.Alpha, screenMode int) *image.R
 			if r != 0 {
 				cOut = colorMap[v]
 			} else {
-				cOut = attenuatedColorMap[v]
+				cOut = colorMapLow[v]
 			}
 			if mask != nil {
 				// RGB mode7

screen/snapshots.go

@@ -36,6 +36,16 @@ func Snapshot(vs VideoSource, screenMode int) *image.RGBA {
 	return snap
 }
 
+// SnapshotPaletted, snapshot of the currently visible screen as a paletted image
+func SnapshotPaletted(vs VideoSource, screenMode int) *image.Paletted {
+	img := Snapshot(vs, screenMode)
+	return palletedFilter(img)
+}
+
+// Color for typical Apple ][ period green P1 phosphor monitors
+// See: https://superuser.com/questions/361297/what-colour-is-the-dark-green-on-old-fashioned-green-screen-computer-displays
+var greenPhosphorColor = color.RGBA{65, 255, 0, 255}
+
 func snapshotByMode(vs VideoSource, videoMode uint16, screenMode int) *image.RGBA {
 	videoBase := videoMode & VideoBaseMask
 	mixMode := videoMode & VideoMixTextMask
@@ -44,9 +54,7 @@ func snapshotByMode(vs VideoSource, videoMode uint16, screenMode int) *image.RGB
 
 	var lightColor color.Color = color.White
 	if screenMode == ScreenModeGreen {
-		// Color for typical Apple ][ period green P1 phosphor monitors
-		// See: https://superuser.com/questions/361297/what-colour-is-the-dark-green-on-old-fashioned-green-screen-computer-displays
-		lightColor = color.RGBA{65, 255, 0, 255}
+		lightColor = greenPhosphorColor
 	}
 
 	applyNTSCFilter := screenMode != ScreenModeGreen
@@ -170,3 +178,21 @@ func linesSeparatedFilter(in *image.RGBA) *image.RGBA {
 	}
 	return out
 }
+
+func palletedFilter(in *image.RGBA) *image.Paletted {
+	bounds := in.Bounds()
+	outBounds := image.Rect(0, 0, bounds.Dx()*2, bounds.Dy())
+	palette := []color.Color{color.Black, color.White, greenPhosphorColor}
+	palette = append(palette, ntscColorMap[:]...)
+	palette = append(palette, attenuatedColorMap[:]...)
+	paletted := image.NewPaletted(outBounds, palette)
+
+	for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
+		for x := bounds.Min.X; x < bounds.Max.X; x++ {
+			c := in.At(x, y)
+			paletted.Set(x*2, y, c)
+			paletted.Set(x*2+1, y, c)
+		}
+	}
+	return paletted
+}