From 4812f2e76e7b2f1c0d057b1a9ad0e419d309ae3f Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Sun, 5 Jun 2016 00:32:57 +0900
Subject: [PATCH] graphics: Reduce calls of glUniformMatrix4fv

---
 image.go      | 22 ++++++++++++++++++++--
 imageparts.go | 19 +++++++++++++++++++
 2 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/image.go b/image.go
index 7a135b11e..7574d73f9 100644
--- a/image.go
+++ b/image.go
@@ -269,6 +269,24 @@ func (i *imageImpl) DrawImage(image *Image, options *DrawImageOptions) error {
 			parts = &wholeImage{image.impl.width, image.impl.height}
 		}
 	}
+	geom := &options.GeoM
+	colorm := &options.ColorM
+	dxf := geom.Element(0, 2)
+	dyf := geom.Element(1, 2)
+	// If possible, avoid using a geometry matrix so that we can reduce calls of
+	// glUniformMatrix4fv.
+	if geom.Element(0, 0) == 1 && geom.Element(1, 0) == 0 && geom.Element(0, 1) == 0 && geom.Element(1, 1) == 1 && (dxf != 0 && dyf != 0) {
+		if dxf == float64(int64(dxf)) && dyf == float64(int64(dyf)) {
+			dx := int(dxf)
+			dy := int(dyf)
+			parts = &transitionImageParts{
+				parts: parts,
+				dx:    dx,
+				dy:    dy,
+			}
+			geom = &GeoM{}
+		}
+	}
 	quads := &textureQuads{parts: parts, width: image.impl.width, height: image.impl.height}
 	// TODO: Reuse one vertices instead of making here, but this would need locking.
 	vertices := make([]int16, parts.Len()*16)
@@ -286,8 +304,8 @@ func (i *imageImpl) DrawImage(image *Image, options *DrawImageOptions) error {
 			return errors.New("ebiten: image is already disposed")
 		}
 		i.pixels = nil
-		m := opengl.CompositeMode(options.CompositeMode)
-		return i.framebuffer.DrawTexture(ui.GLContext(), image.impl.texture, vertices[:16*n], &options.GeoM, &options.ColorM, m)
+		mode := opengl.CompositeMode(options.CompositeMode)
+		return i.framebuffer.DrawTexture(ui.GLContext(), image.impl.texture, vertices[:16*n], geom, colorm, mode)
 	}
 	if theDelayedImageTasks.add(f) {
 		return nil
diff --git a/imageparts.go b/imageparts.go
index 5fb77e925..f124aa463 100644
--- a/imageparts.go
+++ b/imageparts.go
@@ -124,3 +124,22 @@ func (t *textureQuads) vertices(vertices []int16) int {
 	}
 	return n
 }
+
+type transitionImageParts struct {
+	parts ImageParts
+	dx    int
+	dy    int
+}
+
+func (t *transitionImageParts) Len() int {
+	return t.parts.Len()
+}
+
+func (t *transitionImageParts) Dst(index int) (int, int, int, int) {
+	x0, y0, x1, y1 := t.parts.Dst(index)
+	return x0 + t.dx, y0 + t.dy, x1 + t.dx, y1 + t.dy
+}
+
+func (t *transitionImageParts) Src(index int) (int, int, int, int) {
+	return t.parts.Src(index)
+}