From 0efc4c6d59e48a5a29d9c3b96fe106640e4b0f56 Mon Sep 17 00:00:00 2001
From: Thomas Friedel <tomee6@gmail.com>
Date: Thu, 17 May 2018 16:24:29 +0200
Subject: [PATCH] line widths now work more like the html5 canvas

---
 canvas.go | 12 +++++++++++-
 paths.go  | 10 ++++++++--
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/canvas.go b/canvas.go
index 38aebc4..e43fb6a 100644
--- a/canvas.go
+++ b/canvas.go
@@ -33,6 +33,7 @@ type drawState struct {
 	font        *Font
 	fontSize    float64
 	textAlign   textAlign
+	lineAlpha   float64
 	lineWidth   float64
 	lineJoin    lineJoin
 	lineEnd     lineEnd
@@ -474,7 +475,16 @@ func (cv *Canvas) useAlphaShader(style *drawStyle, alphaTexSlot int32) (vertexLo
 
 // SetLineWidth sets the line width for any line drawing calls
 func (cv *Canvas) SetLineWidth(width float64) {
-	cv.state.lineWidth = width
+	if width < 0 {
+		cv.state.lineWidth = 1
+		cv.state.lineAlpha = 0
+	} else if width < 1 {
+		cv.state.lineWidth = 1
+		cv.state.lineAlpha = width
+	} else {
+		cv.state.lineWidth = width
+		cv.state.lineAlpha = 1
+	}
 }
 
 // SetFont sets the font and font size. The font parameter can be a font loaded
diff --git a/paths.go b/paths.go
index dc9c7b8..9fddf57 100644
--- a/paths.go
+++ b/paths.go
@@ -349,7 +349,7 @@ func (cv *Canvas) stroke(path []pathPoint) {
 			float32(lp0[0]), float32(lp0[1]), float32(lp1[0]), float32(lp1[1]), float32(lp3[0]), float32(lp3[1]),
 			float32(lp0[0]), float32(lp0[1]), float32(lp3[0]), float32(lp3[1]), float32(lp2[0]), float32(lp2[1]))
 
-		if p.flags&pathAttach != 0 {
+		if p.flags&pathAttach != 0 && cv.state.lineWidth > 1 {
 			tris = cv.lineJoint(p, p0, p1, p.next, lp0, lp1, lp2, lp3, tris)
 		}
 
@@ -378,7 +378,13 @@ func (cv *Canvas) stroke(path []pathPoint) {
 
 	gli.StencilFunc(gl_EQUAL, 1, 0xFF)
 
+	origAlpha := cv.state.globalAlpha
+	if cv.state.lineAlpha < 1 {
+		cv.state.globalAlpha *= cv.state.lineAlpha
+	}
 	vertex := cv.useShader(&cv.state.stroke)
+	cv.state.globalAlpha = origAlpha
+
 	gli.EnableVertexAttribArray(vertex)
 	gli.VertexAttribPointer(vertex, 2, gl_FLOAT, false, 0, 0)
 	gli.DrawArrays(gl_TRIANGLES, 0, 6)
@@ -681,7 +687,7 @@ func (cv *Canvas) StrokeRect(x, y, w, h float64) {
 	path[1] = pathPoint{pos: v1, tf: v1t, next: v2t, flags: pathAttach}
 	path[2] = pathPoint{pos: v2, tf: v2t, next: v3t, flags: pathAttach}
 	path[3] = pathPoint{pos: v3, tf: v3t, next: v0t, flags: pathAttach}
-	path[4] = pathPoint{pos: v0, tf: v0t}
+	path[4] = pathPoint{pos: v0, tf: v0t, next: v1t, flags: pathAttach}
 	cv.stroke(path[:])
 }