correct processing of signal array in pixel renderers

all SetPixel() function now set VBLANK pixels to 'VideoBlack' via a call
to GetColor(), rather than setting the RGBA values directly. except the
video digest, which remains a special case

this complete work from the previous commit 6826399

bots/chess/videochess.go

@@ -131,9 +131,10 @@ func (obs *observer) SetPixels(sig []signal.SignalAttributes, last int) error {
 	var offset int
 
 	for i := range sig {
-		// handle VBLANK by setting pixels to black
-		if sig[i].VBlank {
-			col = color.RGBA{R: 0, G: 0, B: 0}
+		// handle VBLANK by setting pixels to black. we also manually handle
+		// NoSignal in the same way
+		if sig[i].VBlank || sig[i].Index == signal.NoSignal {
+			col = obs.frameInfo.Spec.GetColor(signal.VideoBlack)
 		} else {
 			col = obs.frameInfo.Spec.GetColor(sig[i].Color)
 		}

bots/spacejockey/spacejockey.go

@@ -100,9 +100,10 @@ func (obs *observer) SetPixels(sig []signal.SignalAttributes, last int) error {
 	var offset int
 
 	for i := range sig {
-		// handle VBLANK by setting pixels to black
-		if sig[i].VBlank {
-			col = color.RGBA{R: 0, G: 0, B: 0}
+		// handle VBLANK by setting pixels to black. we also manually handle
+		// NoSignal in the same way
+		if sig[i].VBlank || sig[i].Index == signal.NoSignal {
+			col = obs.frameInfo.Spec.GetColor(signal.VideoBlack)
 		} else {
 			col = obs.frameInfo.Spec.GetColor(sig[i].Color)
 		}

comparison/comparison.go

@@ -353,9 +353,10 @@ func (cmp *Comparison) SetPixels(sig []signal.SignalAttributes, last int) error
 	var offset int
 
 	for i := range sig {
-		// handle VBLANK by setting pixels to black
-		if sig[i].VBlank {
-			col = color.RGBA{R: 0, G: 0, B: 0}
+		// handle VBLANK by setting pixels to black. we also manually handle
+		// NoSignal in the same way
+		if sig[i].VBlank || sig[i].Index == signal.NoSignal {
+			col = cmp.frameInfo.Spec.GetColor(signal.VideoBlack)
 		} else {
 			col = cmp.frameInfo.Spec.GetColor(sig[i].Color)
 		}

comparison/driver.go

@@ -109,9 +109,10 @@ func (drv *driver) SetPixels(sig []signal.SignalAttributes, last int) error {
 	}
 
 	for i := range sig {
-		// handle VBLANK by setting pixels to black
-		if sig[i].VBlank {
-			col = color.RGBA{R: 0, G: 0, B: 0}
+		// handle VBLANK by setting pixels to black. we also manually handle
+		// NoSignal in the same way
+		if sig[i].VBlank || sig[i].Index == signal.NoSignal {
+			col = drv.frameInfo.Spec.GetColor(signal.VideoBlack)
 		} else {
 			col = drv.frameInfo.Spec.GetColor(sig[i].Color)
 		}

digest/video.go

@@ -18,6 +18,7 @@ package digest
 import (
 	"crypto/sha1"
 	"fmt"
+	"image/color"
 
 	"github.com/jetsetilly/gopher2600/hardware/television"
 	"github.com/jetsetilly/gopher2600/hardware/television/signal"
@@ -108,13 +109,18 @@ func (dig *Video) SetPixels(sig []signal.SignalAttributes, _ int) error {
 	offset := len(dig.digest)
 
 	for _, s := range sig {
-		// ignore invalid signals
+		// ignore invalid signals. this has a consequence that shrunken screen
+		// sizes will have pixel values left over from previous frames. but for
+		// the purposes of the digest this is okay
 		if s.Index == signal.NoSignal {
 			continue
 		}
 
-		// ignore VBLANK and extract the color signal in all situations
-		col := dig.spec.GetColor(s.Color)
+		var col color.RGBA
+
+		// signal processing is unlike other SetPixel() implementations in that
+		// we set the underlying color even if VBLANK is set
+		col = dig.spec.GetColor(s.Color)
 
 		// setting every pixel regardless of vblank value
 		p := dig.pixels[offset : offset+3 : offset+3]

gui/sdlimgui/screen.go

@@ -488,9 +488,10 @@ func (scr *screen) SetPixels(sig []signal.SignalAttributes, last int) error {
 			return nil
 		}
 
-		// handle VBLANK by setting pixels to black
-		if sig[i].VBlank {
-			col = color.RGBA{R: 0, G: 0, B: 0}
+		// handle VBLANK by setting pixels to black. we also manually handle
+		// NoSignal in the same way
+		if sig[i].VBlank || sig[i].Index == signal.NoSignal {
+			col = scr.crit.frameInfo.Spec.GetColor(signal.VideoBlack)
 		} else {
 			col = scr.crit.frameInfo.Spec.GetColor(sig[i].Color)
 		}

hardware/television/protocol.go

@@ -61,17 +61,9 @@ type PixelRenderer interface {
 	// Every signal from SetPixels() therefore corresponds to a pixel in the
 	// bitmap - the first entry always referes to the top-left pixel
 	//
-	// Setting the color of a pixel can be done by extracting the ColorSignal
-	// from the SignalAttributes (see signal package)
-	//
-	// The last parameter indicates the index of the array entry that was most
-	// recently set. This is useful to know when showing televison images when
-	// the emulation is paused. All entries upto and including last are from
-	// teh *current* frame. All entries afterwards are from the *previous*
-	// frame
-	//
-	// If the entry contains signal.NoSignal then that screen pixel has not
-	// been written to recently
+	// If the entry contains signal.NoSignal then that screen pixel has not been
+	// written to recently. However, the bitmap may still need to be updated
+	// with "nil" information if the size of the screen has reduced
 	//
 	// For renderers that are producing an accurate visual image, the pixel
 	// should always be set to video black if VBLANK is on. Some renderers

hardware/television/signal/signal.go

@@ -30,7 +30,10 @@ const VideoBlack ColorSignal = 0xff
 // Index value to indicate that the signal is invalid
 const NoSignal = -1
 
-// SignalAttributes represents the data sent to the television.
+// SignalAttributes represents the data sent to the television
+//
+// When reset the Index field should be set to NoSignal and the Color field
+// should be set to VideoBlack
 type SignalAttributes struct {
 	Index         int
 	VSync         bool

hardware/television/television.go

@@ -844,6 +844,7 @@ func (tv *Television) newFrame() error {
 		// the entire entry
 		tv.signals[i] = signal.SignalAttributes{
 			Index: signal.NoSignal,
+			Color: signal.VideoBlack,
 		}
 	}
 

thumbnailer/anim.go

@@ -317,8 +317,6 @@ func (thmb *Anim) NewScanline(scanline int) error {
 
 // SetPixels implements the television.PixelRenderer interface
 func (thmb *Anim) SetPixels(sig []signal.SignalAttributes, last int) error {
-	var col color.RGBA
-
 	// this adhoc "monitor" system looks for changes in pixels and uses that
 	// information to insert input into the emulation
 	var monitorChanges bool
@@ -328,10 +326,12 @@ func (thmb *Anim) SetPixels(sig []signal.SignalAttributes, last int) error {
 
 	var offset int
 	for i := range sig {
+		var col color.RGBA
 
-		// handle VBLANK by setting pixels to black
-		if sig[i].VBlank {
-			col = color.RGBA{R: 0, G: 0, B: 0}
+		// handle VBLANK by setting pixels to black. we also manually handle
+		// NoSignal in the same way
+		if sig[i].VBlank || sig[i].Index == signal.NoSignal {
+			col = thmb.frameInfo.Spec.GetColor(signal.VideoBlack)
 		} else {
 			col = thmb.frameInfo.Spec.GetColor(sig[i].Color)
 		}

thumbnailer/image.go

@@ -206,13 +206,14 @@ func (thmb *Image) NewScanline(scanline int) error {
 
 // SetPixels implements the television.PixelRenderer interface
 func (thmb *Image) SetPixels(sig []signal.SignalAttributes, last int) error {
-	var col color.RGBA
 	var offset int
-
 	for i := range sig {
-		// handle VBLANK by setting pixels to black
-		if sig[i].VBlank {
-			col = color.RGBA{R: 0, G: 0, B: 0}
+		var col color.RGBA
+
+		// handle VBLANK by setting pixels to black. we also manually handle
+		// NoSignal in the same way
+		if sig[i].VBlank || sig[i].Index == signal.NoSignal {
+			col = thmb.frameInfo.Spec.GetColor(signal.VideoBlack)
 		} else {
 			col = thmb.frameInfo.Spec.GetColor(sig[i].Color)
 		}