unified Clear and ClearRect

backend/backendbase/base.go

@@ -14,7 +14,7 @@ type Backend interface {
 	LoadLinearGradient(data *LinearGradientData) LinearGradient
 	LoadRadialGradient(data *RadialGradientData) RadialGradient
 
-	ClearRect(x, y, w, h int)
+	// ClearRect(x, y, w, h int)
 	Clear(pts [4][2]float64)
 	Fill(style *FillStyle, pts [][2]float64)
 	DrawImage(dimg Image, sx, sy, sw, sh, dx, dy, dw, dh float64, alpha float64)

backend/gogl/fill.go

@@ -9,15 +9,22 @@ import (
 	"github.com/tfriedel6/canvas/backend/backendbase"
 )
 
-// ClearRect sets the color of the rectangle to transparent black
-func (b *GoGLBackend) ClearRect(x, y, w, h int) {
-	gl.Scissor(int32(x), int32(b.h-y-h), int32(w), int32(h))
-	gl.ClearColor(0, 0, 0, 0)
-	gl.Clear(gl.COLOR_BUFFER_BIT)
-	// cv.applyScissor()
-}
-
 func (b *GoGLBackend) Clear(pts [4][2]float64) {
+	// first check if the four points are aligned to form a nice rectangle, which can be more easily
+	// cleared using glScissor and glClear
+	aligned := pts[0][0] == pts[1][0] && pts[2][0] == pts[3][0] && pts[0][1] == pts[3][1] && pts[1][1] == pts[2][1]
+	if !aligned {
+		aligned = pts[0][0] == pts[3][0] && pts[1][0] == pts[2][0] && pts[0][1] == pts[1][1] && pts[2][1] == pts[3][1]
+	}
+	if aligned {
+		minX := math.Floor(math.Min(pts[0][0], pts[2][0]))
+		maxX := math.Ceil(math.Max(pts[0][0], pts[2][0]))
+		minY := math.Floor(math.Min(pts[0][1], pts[2][1]))
+		maxY := math.Ceil(math.Max(pts[0][1], pts[2][1]))
+		b.clearRect(int(minX), int(minY), int(maxX)-int(minX), int(maxY)-int(minY))
+		return
+	}
+
 	data := [8]float32{
 		float32(pts[0][0]), float32(pts[0][1]),
 		float32(pts[1][0]), float32(pts[1][1]),
@@ -46,6 +53,13 @@ func (b *GoGLBackend) Clear(pts [4][2]float64) {
 	gl.Enable(gl.BLEND)
 }
 
+func (b *GoGLBackend) clearRect(x, y, w, h int) {
+	gl.Scissor(int32(x), int32(b.h-y-h), int32(w), int32(h))
+	gl.ClearColor(0, 0, 0, 0)
+	gl.Clear(gl.COLOR_BUFFER_BIT)
+	// cv.applyScissor()
+}
+
 func (b *GoGLBackend) Fill(style *backendbase.FillStyle, pts [][2]float64) {
 	if style.Blur > 0 {
 		b.offscr1.alpha = true

backend/gogl/gogl.go

@@ -414,6 +414,8 @@ func (b *GoGLBackend) enableTextureRenderTarget(offscr *offscreenBuffer) {
 		}
 		gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST)
 		gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST)
+		gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE)
+		gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE)
 
 		gl.GenFramebuffers(1, &offscr.frameBuf)
 		gl.BindFramebuffer(gl.FRAMEBUFFER, offscr.frameBuf)

paths.go

@@ -536,17 +536,10 @@ func (cv *Canvas) FillRect(x, y, w, h float64) {
 func (cv *Canvas) ClearRect(x, y, w, h float64) {
 	cv.activate()
 
-	if cv.state.transform == matIdentity() {
-		cv.b.ClearRect(int(x+0.5), int(y+0.5), int(w+0.5), int(h+0.5))
-		cv.applyScissor()
-		return
-	}
-
 	p0 := cv.tf(vec{x, y})
 	p1 := cv.tf(vec{x, y + h})
 	p2 := cv.tf(vec{x + w, y + h})
 	p3 := cv.tf(vec{x + w, y})
-
 	data := [4][2]float64{{p0[0], p0[1]}, {p1[0], p1[1]}, {p2[0], p2[1]}, {p3[0], p3[1]}}
 
 	cv.b.Clear(data)