Demonstration of alpha blending modes

2 files changed, 41 insertions, 9 deletions

diff --git a/fpdf.go b/fpdf.go
index 24db0be..f526821 100644
--- a/fpdf.go
+++ b/fpdf.go
@@ -841,7 +841,7 @@ func (f *Fpdf) Arc(x, y, rx, ry, degRotate, degStart, degEnd float64, styleStr s
 // To reset normal rendering after applying a blending mode, call this method
 // with alpha set to 1.0 and blendModeStr set to "Normal".
 //
-// See tutorial 12 for an example of this function.
+// See tutorial 12 for an example of this function, including samples of each blending mode.
 func (f *Fpdf) SetAlpha(alpha float64, blendModeStr string) {
 	if f.err != nil {
 		return
diff --git a/fpdf_test.go b/fpdf_test.go
index 08dca43..5e2e7a8 100644
--- a/fpdf_test.go
+++ b/fpdf_test.go
@@ -707,16 +707,48 @@ func ExampleFpdf_tutorial11() {
 
 // Transparency
 func ExampleFpdf_tutorial12() {
+	const (
+		gapX  = 10.0
+		gapY  = 9.0
+		rectW = 40.0
+		rectH = 58.0
+		pageW = 210
+		pageH = 297
+	)
+	modeList := []string{"Normal", "Multiply", "Screen", "Overlay",
+		"Darken", "Lighten", "ColorDodge", "ColorBurn", "HardLight", "SoftLight",
+		"Difference", "Exclusion", "Hue", "Saturation", "Color", "Luminosity"}
 	pdf := New("", "", "", FONT_DIR)
-	pdf.SetFont("Helvetica", "", 48)
-	pdf.SetLineWidth(4)
-	pdf.SetFillColor(180, 180, 180)
+	pdf.SetLineWidth(2)
+	pdf.SetAutoPageBreak(false, 0)
 	pdf.AddPage()
-	pdf.SetXY(55, 60)
-	pdf.CellFormat(100, 40, "Go", "1", 0, "C", true, 0, "")
-	pdf.SetAlpha(0.5, "Normal")
-	pdf.Image(IMG_DIR+"/golang-gopher.png", 30, 10, 150, 0, false, "", 0, "")
-	pdf.SetAlpha(1.0, "Normal")
+	pdf.SetFont("Helvetica", "", 18)
+	pdf.SetXY(0, gapY)
+	pdf.SetTextColor(0, 0, 0)
+	pdf.CellFormat(pageW, gapY, "Alpha Blending Modes", "", 0, "C", false, 0, "")
+	j := 0
+	y := 3 * gapY
+	for col := 0; col < 4; col++ {
+		x := gapX
+		for row := 0; row < 4; row++ {
+			pdf.Rect(x, y, rectW, rectH, "D")
+			pdf.SetFont("Helvetica", "B", 12)
+			pdf.SetFillColor(0, 0, 0)
+			pdf.SetTextColor(250, 250, 230)
+			pdf.SetXY(x, y+rectH-4)
+			pdf.CellFormat(rectW, 5, modeList[j], "", 0, "C", true, 0, "")
+			pdf.SetFont("Helvetica", "I", 150)
+			pdf.SetTextColor(80, 80, 120)
+			pdf.SetXY(x, y+2)
+			pdf.CellFormat(rectW, rectH, "A", "", 0, "C", false, 0, "")
+			pdf.SetAlpha(0.5, modeList[j])
+			pdf.Image(IMG_DIR+"/golang-gopher.png", x-gapX, y, rectW+2*gapX, 0, false, "", 0, "")
+			pdf.SetAlpha(1.0, "Normal")
+			x += rectW + gapX
+			j++
+		}
+		y += rectH + gapY
+	}
 	pdf.OutputAndClose(docWriter(pdf, 12))
 	// Output:
 	// Successfully generated pdf/tutorial12.pdf