RF noise reduced to zero during screenshots

the TV image may noticeably change brightness during the duration screenshot
because of the absence of noise

Author: JetSetIlly

gui/sdlimgui/gl32.go

@@ -193,7 +193,6 @@ func (rnd *gl32) render() {
 			} else {
 				// texture id
 				id := cmd.TextureID()
-
 				env.textureID = uint32(id)
 
 				// select shader program to use

gui/sdlimgui/gl32_crtseq.go

@@ -106,7 +106,7 @@ func newCRTSequencer(img *SdlImgui) *crtSequencer {
 		sharpenShader:  newSharpenShader(),
 		phosphorShader: newPhosphorShader(),
 		blurShader:     newBlurShader(),
-		effectsShader:  newEffectsShader(),
+		effectsShader:  newEffectsShader(img.rnd),
 		colorShader:    newColorShader(),
 	}
 	return sh

gui/sdlimgui/gl32_crtseq_effects.go

@@ -54,10 +54,22 @@ type effectsShader struct {
 	rotation   int32
 	screenshot int32
 	time       int32
+
+	isScrsht isScreenshotting
+}
+
+// used by the effects shader to determine if a screenshot is taking place. if
+// it is then specific effects settings are used with the aim of improving the
+// screenshot image
+type isScreenshotting interface {
+	isScreenshotting() bool
 }
 
-func newEffectsShader() shaderProgram {
-	sh := &effectsShader{}
+func newEffectsShader(isScrsht isScreenshotting) shaderProgram {
+	sh := &effectsShader{
+		isScrsht: isScrsht,
+	}
+
 	sh.createProgram(string(shaders.StraightVertexShader), string(shaders.CRTEffectsFragShader))
 
 	sh.screenDim = gl.GetUniformLocation(sh.handle, gl.Str("ScreenDim"+"\x00"))
@@ -125,4 +137,9 @@ func (sh *effectsShader) setAttributesArgs(env shaderEnvironment, numScanlines i
 	gl.Uniform1i(sh.rotation, int32(rotation))
 	gl.Uniform1i(sh.screenshot, boolToInt32(screenshot))
 	gl.Uniform1f(sh.time, float32(time.Now().Nanosecond())/100000000.0)
+
+	// no noise when a screenshot is taking place
+	if sh.isScrsht.isScreenshotting() {
+		gl.Uniform1f(sh.rfNoiseLevel, float32(0))
+	}
 }