Optimize exp/draw/x11 flusher inner loop.

On my laptop, time to prepare and write 800x600 pixels over the
socket falls from 125-ish ms to 80-ish ms.

Thanks to Roger Peppe for the suggestion.

R=r
CC=golang-dev
https://golang.org/cl/1228044

diff --git a/src/pkg/exp/draw/x11/conn.go b/src/pkg/exp/draw/x11/conn.go
index f1a3dca1c6ce03d53290a3e52301d15ddd974916..3579a24c38e31f9f094057082070c6794b01f39c 100644 (file)
--- a/src/pkg/exp/draw/x11/conn.go
+++ b/src/pkg/exp/draw/x11/conn.go
@@ -91,18 +91,18 @@ func (c *conn) flusher() {
                                close(c.flush)
                                return
                        }
+                       p := c.img.Pixel[y]
                        for x := 0; x < w; {
                                nx := w - x
                                if nx > len(c.flushBuf1)/4 {
                                        nx = len(c.flushBuf1) / 4
                                }
-                               for i := 0; i < nx; i++ {
-                                       r, g, b, _ := c.img.At(x, y).RGBA()
-                                       c.flushBuf1[4*i+0] = uint8(b >> 24)
-                                       c.flushBuf1[4*i+1] = uint8(g >> 24)
-                                       c.flushBuf1[4*i+2] = uint8(r >> 24)
-                                       x++
+                               for i, rgba := range p[x : x+nx] {
+                                       c.flushBuf1[4*i+0] = rgba.B
+                                       c.flushBuf1[4*i+1] = rgba.G
+                                       c.flushBuf1[4*i+2] = rgba.R
                                }
+                               x += nx
                                _, err := c.w.Write(c.flushBuf1[0 : 4*nx])
                                if err != nil {
                                        close(c.flush)