From aea2e491c3cfb5e61ee626cb66083357d66cbf07 Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Tue, 12 Dec 2017 03:27:56 +0900
Subject: [PATCH] graphics: Temporary hack for mobile browers

roundTexel doesn't work well on moible browsers
---
 internal/graphics/shader.go | 30 ++++++++++++++++++++++++++++--
 1 file changed, 28 insertions(+), 2 deletions(-)

diff --git a/internal/graphics/shader.go b/internal/graphics/shader.go
index 01ac96192..5a88a50cb 100644
--- a/internal/graphics/shader.go
+++ b/internal/graphics/shader.go
@@ -14,6 +14,12 @@
 
 package graphics
 
+import (
+	"strings"
+
+	"github.com/hajimehoshi/ebiten/internal/web"
+)
+
 type shaderId int
 
 const (
@@ -22,11 +28,19 @@ const (
 )
 
 func shader(id shaderId) string {
-	return shaders[id]
+	s := shaders[id]
+	defs := []string{}
+	if web.IsMobileBrowser() {
+		defs = append(defs, "#define IS_MOBILE_BROWSER")
+	}
+	s = strings.Replace(s, "{{Definitions}}", strings.Join(defs, "\n"), -1)
+	return s
 }
 
 var shaders = map[shaderId]string{
 	shaderVertexModelview: `
+{{Definitions}}
+
 uniform mat4 projection_matrix;
 attribute vec2 vertex;
 attribute vec4 tex_coord;
@@ -60,17 +74,28 @@ precision mediump float;
 #define highp
 #endif
 
+{{Definitions}}
+
 uniform sampler2D texture;
 uniform mat4 color_matrix;
 uniform vec4 color_matrix_translation;
-uniform int filter_type;
 uniform vec2 source_size;
+uniform int filter_type;
 
 varying vec2 varying_tex_coord;
 varying vec2 varying_tex_coord_min;
 varying vec2 varying_tex_coord_max;
 
 vec2 roundTexel(vec2 p) {
+#if defined(IS_MOBILE_BROWSER)
+  // This is a temporary hack: on mobile browsers like Android Chrome,
+  // the code to round a float might cause unexpected behavior.
+  // This is confirmed with rendering a relatively large (e.g. 4096x512) image
+  // with specifying a source rectangle near its edges.
+  // TODO: examples/moire doesn't work anyway.
+  // TODO: Does this function work on an Android native app?
+  return p;
+#else
   vec2 factor = 1.0 / (source_size * 256.0);
   if (factor.x > 0.0) {
     p.x -= mod(p.x + factor.x * 0.5, factor.x) - factor.x * 0.5;
@@ -79,6 +104,7 @@ vec2 roundTexel(vec2 p) {
     p.y -= mod(p.y + factor.y * 0.5, factor.y) - factor.y * 0.5;
   }
   return p;
+#endif
 }
 
 vec4 getColorAt(vec2 pos) {