Use dep to vendor things

vendor/github.com/faiface/pixel/interface.go

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+package pixel
+
+import "image/color"
+
+// Target is something that can be drawn onto, such as a window, a canvas, and so on.
+//
+// You can notice, that there are no "drawing" methods in a Target. That's because all drawing
+// happens indirectly through Triangles and Picture instances generated via MakeTriangles and
+// MakePicture method.
+type Target interface {
+	// MakeTriangles generates a specialized copy of the provided Triangles.
+	//
+	// When calling Draw method on the returned TargetTriangles, the TargetTriangles will be
+	// drawn onto the Target that generated them.
+	//
+	// Note, that not every Target has to recognize all possible types of Triangles. Some may
+	// only recognize TrianglesPosition and TrianglesColor and ignore all other properties (if
+	// present) when making new TargetTriangles. This varies from Target to Target.
+	MakeTriangles(Triangles) TargetTriangles
+
+	// MakePicture generates a specialized copy of the provided Picture.
+	//
+	// When calling Draw method on the returned TargetPicture, the TargetPicture will be drawn
+	// onto the Target that generated it together with the TargetTriangles supplied to the Draw
+	// method.
+	MakePicture(Picture) TargetPicture
+}
+
+// BasicTarget is a Target with additional basic adjustment methods.
+type BasicTarget interface {
+	Target
+
+	// SetMatrix sets a Matrix that every point will be projected by.
+	SetMatrix(Matrix)
+
+	// SetColorMask sets a color that will be multiplied with the TrianglesColor property of all
+	// Triangles.
+	SetColorMask(color.Color)
+}
+
+// Triangles represents a list of vertices, where each three vertices form a triangle. (First,
+// second and third is the first triangle, fourth, fifth and sixth is the second triangle, etc.)
+type Triangles interface {
+	// Len returns the number of vertices. The number of triangles is the number of vertices
+	// divided by 3.
+	Len() int
+
+	// SetLen resizes Triangles to len vertices. If Triangles B were obtained by calling Slice
+	// method on Triangles A, the relationship between A and B is undefined after calling SetLen
+	// on either one of them.
+	SetLen(len int)
+
+	// Slice returns a sub-Triangles of this Triangles, covering vertices in range [i, j).
+	//
+	// If Triangles B were obtained by calling Slice(4, 9) on Triangles A, then A and B must
+	// share the same underlying data. Modifying B must change the contents of A in range
+	// [4, 9). The vertex with index 0 at B is the vertex with index 4 in A, and so on.
+	//
+	// Returned Triangles must have the same underlying type.
+	Slice(i, j int) Triangles
+
+	// Update copies vertex properties from the supplied Triangles into this Triangles.
+	//
+	// Properies not supported by these Triangles should be ignored. Properties not supported by
+	// the supplied Triangles should be left untouched.
+	//
+	// The two Triangles must have the same Len.
+	Update(Triangles)
+
+	// Copy creates an exact independent copy of this Triangles (with the same underlying type).
+	Copy() Triangles
+}
+
+// TargetTriangles are Triangles generated by a Target with MakeTriangles method. They can be drawn
+// onto that (no other) Target.
+type TargetTriangles interface {
+	Triangles
+
+	// Draw draws Triangles onto an associated Target.
+	Draw()
+}
+
+// TrianglesPosition specifies Triangles with Position property.
+type TrianglesPosition interface {
+	Triangles
+	Position(i int) Vec
+}
+
+// TrianglesColor specifies Triangles with Color property.
+type TrianglesColor interface {
+	Triangles
+	Color(i int) RGBA
+}
+
+// TrianglesPicture specifies Triangles with Picture propery.
+//
+// The first value returned from Picture method is Picture coordinates. The second one specifies the
+// weight of the Picture. Value of 0 means, that Picture should be completely ignored, 1 means that
+// is should be fully included and anything in between means anything in between.
+type TrianglesPicture interface {
+	Triangles
+	Picture(i int) (pic Vec, intensity float64)
+}
+
+// Picture represents a rectangular area of raster data, such as a color. It has Bounds which
+// specify the rectangle where data is located.
+type Picture interface {
+	// Bounds returns the rectangle of the Picture. All data is located witih this rectangle.
+	// Querying properties outside the rectangle should return default value of that property.
+	Bounds() Rect
+}
+
+// TargetPicture is a Picture generated by a Target using MakePicture method. This Picture can be drawn onto
+// that (no other) Target together with a TargetTriangles generated by the same Target.
+//
+// The TargetTriangles specify where, shape and how the Picture should be drawn.
+type TargetPicture interface {
+	Picture
+
+	// Draw draws the supplied TargetTriangles (which must be generated by the same Target as
+	// this TargetPicture) with this TargetPicture. The TargetTriangles should utilize the data
+	// from this TargetPicture in some way.
+	Draw(TargetTriangles)
+}
+
+// PictureColor specifies Picture with Color property, so that every position inside the Picture's
+// Bounds has a color.
+//
+// Positions outside the Picture's Bounds must return full transparent (Alpha(0)).
+type PictureColor interface {
+	Picture
+	Color(at Vec) RGBA
+}