From d4042a5cfa6fe02258f6abb1d6465d18346adc28 Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Wed, 12 Aug 2020 02:12:32 +0900
Subject: [PATCH] ebiten: Bug fix: Source regions should not be passed when not
 needed

The source region information affects the condition of merging
graphics commands. To avoid performance issues by the big number of
graphcis commands, do not pass the source region whenever possible.

Fixes #1293
---
 image.go                    | 28 ++++++++++++++++++----------
 internal/shareable/image.go |  8 ++++++--
 2 files changed, 24 insertions(+), 12 deletions(-)

diff --git a/image.go b/image.go
index ff2bb32c1..69c4ba44a 100644
--- a/image.go
+++ b/image.go
@@ -271,11 +271,15 @@ func (i *Image) DrawImage(img *Image, options *DrawImageOptions) error {
 	is := graphics.QuadIndices()
 
 	var sr driver.Region
-	sr = driver.Region{
-		X:      float32(bounds.Min.X),
-		Y:      float32(bounds.Min.Y),
-		Width:  float32(bounds.Dx()),
-		Height: float32(bounds.Dy()),
+	// Pass the source region only when the shader is used, since this affects the condition of merging graphics
+	// commands (#1293).
+	if options.Shader != nil {
+		sr = driver.Region{
+			X:      float32(bounds.Min.X),
+			Y:      float32(bounds.Min.Y),
+			Width:  float32(bounds.Dx()),
+			Height: float32(bounds.Dy()),
+		}
 	}
 
 	srcs := [graphics.ShaderImageNum]*mipmap.Mipmap{img.mipmap}
@@ -430,11 +434,15 @@ func (i *Image) DrawTriangles(vertices []Vertex, indices []uint16, img *Image, o
 
 	var sr driver.Region
 	b := img.Bounds()
-	sr = driver.Region{
-		X:      float32(b.Min.X),
-		Y:      float32(b.Min.Y),
-		Width:  float32(b.Dx()),
-		Height: float32(b.Dy()),
+	// Pass the source region only when the shader is used, since this affects the condition of merging graphics
+	// commands (#1293).
+	if options.Shader != nil || options.Address != AddressUnsafe {
+		sr = driver.Region{
+			X:      float32(b.Min.X),
+			Y:      float32(b.Min.Y),
+			Width:  float32(b.Dx()),
+			Height: float32(b.Dy()),
+		}
 	}
 
 	var srcs [graphics.ShaderImageNum]*mipmap.Mipmap
diff --git a/internal/shareable/image.go b/internal/shareable/image.go
index 4cb3fa6f6..0ae46ee7b 100644
--- a/internal/shareable/image.go
+++ b/internal/shareable/image.go
@@ -337,8 +337,12 @@ func (i *Image) DrawTriangles(srcs [graphics.ShaderImageNum]*Image, vertices []f
 			vertices[i*graphics.VertexFloatNum+2] += oxf
 			vertices[i*graphics.VertexFloatNum+3] += oyf
 		}
-		sourceRegion.X += oxf
-		sourceRegion.Y += oyf
+		// sourceRegion can be delibarately empty when this is not needed in order to avoid unexpected
+		// performance issue (#1293).
+		if sourceRegion.Width != 0 && sourceRegion.Height != 0 {
+			sourceRegion.X += oxf
+			sourceRegion.Y += oyf
+		}
 	}
 
 	var offsets [graphics.ShaderImageNum - 1][2]float32