Added gradient drawing support for ImageMagick 6. (#162)

* Added gradient drawing support.

* Update travis to use ImageMagick-6.9.9-40

* Update travis yml to derive ImageMagick version from external dashboard

* Remove unnecessary containers.

examples/gradient/main.go

@@ -0,0 +1,24 @@
+package main
+
+import (
+	"gopkg.in/gographics/imagick.v2/imagick"
+)
+
+// Demonstrate creating a gradient image including artifact mods.
+func main() {
+	imagick.Initialize()
+	defer imagick.Terminate()
+
+	mw := imagick.NewMagickWand()
+	mw.SetSize(300,300)
+
+	fc := imagick.NewPixelWand()
+	fc.SetColor("none")
+	mw.NewImage(300, 300, fc)
+	mw.SetImageArtifact("gradient:angle", "35")
+
+	mw.GradientImage(imagick.GRADIENT_TYPE_LINEAR, imagick.SPREAD_METHOD_PAD, "#ff0000", "#0000ff")
+
+	mw.WriteImage("out.png")
+
+}

imagick/gradient_type.go

@@ -0,0 +1,14 @@
+package imagick
+
+/*
+#include <wand/MagickWand.h>
+*/
+import "C"
+
+type GradientType int
+
+const (
+	GRADIENT_TYPE_UNDEFINED GradientType = C.UndefinedGradient
+	GRADIENT_TYPE_LINEAR    GradientType = C.LinearGradient
+	GRADIENT_TYPE_RADIAL    GradientType = C.RadialGradient
+)

imagick/magick_wand_image.go

@@ -1550,6 +1550,23 @@ func (mw *MagickWand) GetImageTotalInkDensity() float64 {
 	return ret
 }
 
+func (mw *MagickWand) GradientImage(gradientType GradientType, spreadMethod SpreadMethod, startColor string, stopColor string) error {
+	ppStart := C.PixelPacket{}
+	ppStop := C.PixelPacket{}
+
+	pw := NewPixelWand()
+	defer pw.Destroy()
+	pw.SetColor(startColor)
+	C.SetPixelViaMagickPixel(mw.GetImageFromMagickWand().img, pw.GetMagickColor().mpp, &ppStart)
+	pw.SetColor(stopColor)
+	C.SetPixelViaMagickPixel(mw.GetImageFromMagickWand().img, pw.GetMagickColor().mpp, &ppStop)
+	ok := C.GradientImage(mw.GetImageFromMagickWand().img,
+		C.GradientType(gradientType), C.SpreadMethod(spreadMethod),
+		&ppStart, &ppStop)
+	runtime.KeepAlive(mw)
+	return mw.getLastErrorIfFailed(ok)
+}
+
 // Replaces colors in the image from a Hald color lookup table. A Hald color
 // lookup table is a 3-dimensional color cube mapped to 2 dimensions. Create
 // it with the HALD coder. You can apply any color transformation to the Hald

imagick/spread_method.go

@@ -0,0 +1,15 @@
+package imagick
+
+/*
+#include <wand/MagickWand.h>
+*/
+import "C"
+
+type SpreadMethod int
+
+const (
+	SPREAD_METHOD_UNDEFINED SpreadMethod = C.UndefinedGradient
+	SPREAD_METHOD_PAD       SpreadMethod = C.PadSpread
+	SPREAD_METHOD_REFLECT   SpreadMethod = C.ReflectSpread
+	SPREAD_METHOD_REPEAT    SpreadMethod = C.RepeatSpread
+)