From 20842979997c90fee2ef3417854617dc5e1e621c Mon Sep 17 00:00:00 2001
From: George Stark <stark.georgy@gmail.com>
Date: Tue, 30 Mar 2021 13:30:23 +0300
Subject: [PATCH] add method to change drawing interpolator

default interpolator used for drawing text and images is draw.BiLinear
and it's rather slow against e.g. draw.NearestNeighbor
The difference is significant especially on weak hardware
e.g. on raspberry pi zero (ARMv6) drawing short string can be 10-16 times
faster with draw.NearestNeighbor

Signed-off-by: George Stark <stark.georgy@gmail.com>
---
 context.go | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/context.go b/context.go
index 1ddb09f..5cb7ddc 100644
--- a/context.go
+++ b/context.go
@@ -77,6 +77,7 @@ type Context struct {
 	fontHeight    float64
 	matrix        Matrix
 	stack         []*Context
+	interpolator  draw.Interpolator
 }
 
 // NewContext creates a new image.RGBA with the specified width and height
@@ -109,9 +110,14 @@ func NewContextForRGBA(im *image.RGBA) *Context {
 		fontFace:      basicfont.Face7x13,
 		fontHeight:    13,
 		matrix:        Identity(),
+		interpolator:  draw.BiLinear,
 	}
 }
 
+func (dc *Context) SetInterpolator(interpolator draw.Interpolator) {
+	dc.interpolator = interpolator
+}
+
 // GetCurrentPoint will return the current point and if there is a current point.
 // The point will have been transformed by the context's transformation matrix.
 func (dc *Context) GetCurrentPoint() (Point, bool) {
@@ -673,7 +679,7 @@ func (dc *Context) DrawImageAnchored(im image.Image, x, y int, ax, ay float64) {
 	s := im.Bounds().Size()
 	x -= int(ax * float64(s.X))
 	y -= int(ay * float64(s.Y))
-	transformer := draw.BiLinear
+	transformer := dc.interpolator
 	fx, fy := float64(x), float64(y)
 	m := dc.matrix.Translate(fx, fy)
 	s2d := f64.Aff3{m.XX, m.XY, m.X0, m.YX, m.YY, m.Y0}
@@ -728,7 +734,7 @@ func (dc *Context) drawString(im *image.RGBA, s string, x, y float64) {
 			continue
 		}
 		sr := dr.Sub(dr.Min)
-		transformer := draw.BiLinear
+		transformer := dc.interpolator
 		fx, fy := float64(dr.Min.X), float64(dr.Min.Y)
 		m := dc.matrix.Translate(fx, fy)
 		s2d := f64.Aff3{m.XX, m.XY, m.X0, m.YX, m.YY, m.Y0}