From f8bf1e9e53032848b48bb2cb49cf92184d23223b Mon Sep 17 00:00:00 2001
From: Pierre-Yves Rollo <dev@pyrollo.com>
Date: Tue, 24 Sep 2019 17:06:52 +0200
Subject: [PATCH] Use a very simplified image downsampling for optimization
 purpose

---
 tilerenderer/renderer.go | 57 ++++++++++++++++++++++------------------
 1 file changed, 32 insertions(+), 25 deletions(-)

diff --git a/tilerenderer/renderer.go b/tilerenderer/renderer.go
index 39b75ac..324e3ad 100644
--- a/tilerenderer/renderer.go
+++ b/tilerenderer/renderer.go
@@ -14,8 +14,6 @@ import (
 	"mapserver/tiledb"
 	"strconv"
 	"time"
-
-	"github.com/disintegration/imaging"
 	"github.com/sirupsen/logrus"
 
 	"github.com/prometheus/client_golang/prometheus"
@@ -29,6 +27,33 @@ type TileRenderer struct {
 	Eventbus         *eventbus.Eventbus
 }
 
+func resizeImage(src *image.NRGBA, tgt *image.NRGBA, xoffset int, yoffset int) {
+	if src == nil {
+		return
+	}
+	w := src.Bounds().Dy() >> 1
+	h := src.Bounds().Dx() >> 1
+	sinc := src.Bounds().Dy() * 4
+	tinc := tgt.Bounds().Dx() * 4
+
+	for y := 0; y < h; y++ {
+		six := y * sinc * 2
+		tix := 4 * xoffset + (yoffset + y) * tinc
+		for x := 0; x < w; x++ {
+			r := (uint16(src.Pix[six]) + uint16(src.Pix[six+4]) + uint16(src.Pix[six+sinc]) + uint16(src.Pix[six+sinc+4])) >> 2
+			g := (uint16(src.Pix[six+1]) + uint16(src.Pix[six+5]) + uint16(src.Pix[six+sinc+1]) + uint16(src.Pix[six+sinc+5])) >> 2
+			b := (uint16(src.Pix[six+2]) + uint16(src.Pix[six+6]) + uint16(src.Pix[six+sinc+2]) + uint16(src.Pix[six+sinc+6])) >> 2
+			a := (uint16(src.Pix[six+3]) + uint16(src.Pix[six+7]) + uint16(src.Pix[six+sinc+3]) + uint16(src.Pix[six+sinc+7])) >> 2
+			tgt.Pix[tix] = uint8(r)
+			tgt.Pix[tix+1] = uint8(g)
+			tgt.Pix[tix+2] = uint8(b)
+			tgt.Pix[tix+3] = uint8(a)
+			tix+=4
+			six+=8
+		}
+	}
+}
+
 func NewTileRenderer(mapblockrenderer *mapblockrenderer.MapBlockRenderer,
 	tdb *tiledb.TileDB,
 	dba db.DBAccessor,
@@ -45,6 +70,7 @@ func NewTileRenderer(mapblockrenderer *mapblockrenderer.MapBlockRenderer,
 
 const (
 	IMG_SIZE = 256
+	SUB_IMG_SIZE = IMG_SIZE >> 1
 )
 
 func (tr *TileRenderer) Render(tc *coords.TileCoords) ([]byte, error) {
@@ -186,29 +212,10 @@ func (tr *TileRenderer) renderImage(tc *coords.TileCoords, recursionDepth int) (
 		},
 	)
 
-	rect := image.Rect(0, 0, 128, 128)
-	if upperLeft != nil {
-		resizedImg := imaging.Resize(upperLeft, 128, 128, imaging.Lanczos)
-		draw.Draw(img, rect, resizedImg, image.ZP, draw.Src)
-	}
-
-	rect = image.Rect(128, 0, 256, 128)
-	if upperRight != nil {
-		resizedImg := imaging.Resize(upperRight, 128, 128, imaging.Lanczos)
-		draw.Draw(img, rect, resizedImg, image.ZP, draw.Src)
-	}
-
-	rect = image.Rect(0, 128, 128, 256)
-	if lowerLeft != nil {
-		resizedImg := imaging.Resize(lowerLeft, 128, 128, imaging.Lanczos)
-		draw.Draw(img, rect, resizedImg, image.ZP, draw.Src)
-	}
-
-	rect = image.Rect(128, 128, 256, 256)
-	if lowerRight != nil {
-		resizedImg := imaging.Resize(lowerRight, 128, 128, imaging.Lanczos)
-		draw.Draw(img, rect, resizedImg, image.ZP, draw.Src)
-	}
+	resizeImage(upperLeft, img, 0, 0)
+	resizeImage(upperRight, img, SUB_IMG_SIZE, 0)
+	resizeImage(lowerLeft, img, 0, SUB_IMG_SIZE)
+	resizeImage(lowerRight, img, SUB_IMG_SIZE, SUB_IMG_SIZE)
 
 	t = time.Now()
 	quadresize := t.Sub(start)