From 62070f11d5c8b9c55c53479c7e133d06ca676323 Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Tue, 15 Jul 2025 15:26:08 -0700
Subject: [PATCH] =?UTF-8?q?GBA=20Video:=20Disable=20window=20interpolation?=
 =?UTF-8?q?=20at=201=C3=97=20scale=20(fixes=20#1810)?=
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---
 CHANGES                                  | 1 +
 include/mgba/internal/gba/renderers/gl.h | 1 +
 src/gba/renderers/gl.c                   | 5 ++++-
 3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/CHANGES b/CHANGES
index 9121261b7..5b093035b 100644
--- a/CHANGES
+++ b/CHANGES
@@ -59,6 +59,7 @@ Misc:
  - GBA Memory: Improve VRAM access stall cycle estimation
  - GBA SIO: Rewrite lockstep driver for improved stability
  - GBA Video: Add special circlular window handling in OpenGL renderer
+ - GBA Video: Disable window interpolation at 1× scale (fixes mgba.io/i/1810)
  - Libretro: Add Super Game Boy Color support (closes mgba.io/i/3188)
  - mGUI: Enable auto-softpatching (closes mgba.io/i/2899)
  - mGUI: Persist fast forwarding after closing menu (fixes mgba.io/i/2414)
diff --git a/include/mgba/internal/gba/renderers/gl.h b/include/mgba/internal/gba/renderers/gl.h
index 74baec41e..679df15b9 100644
--- a/include/mgba/internal/gba/renderers/gl.h
+++ b/include/mgba/internal/gba/renderers/gl.h
@@ -120,6 +120,7 @@ enum {
 	GBA_GL_WIN_WIN1,
 	GBA_GL_WIN_CIRCLE0,
 	GBA_GL_WIN_CIRCLE1,
+	GBA_GL_WIN_DISABLE_INTERP,
 
 	GBA_GL_FINALIZE_SCALE = 2,
 	GBA_GL_FINALIZE_LAYERS,
diff --git a/src/gba/renderers/gl.c b/src/gba/renderers/gl.c
index dbff67e4e..405c97f79 100644
--- a/src/gba/renderers/gl.c
+++ b/src/gba/renderers/gl.c
@@ -493,6 +493,7 @@ static const struct GBAVideoGLUniform _uniformsWindow[] = {
 	{ "win1", GBA_GL_WIN_WIN1, },
 	{ "circle0", GBA_GL_WIN_CIRCLE0, },
 	{ "circle1", GBA_GL_WIN_CIRCLE1, },
+	{ "disableInterp", GBA_GL_WIN_DISABLE_INTERP, },
 	{ 0 }
 };
 
@@ -505,6 +506,7 @@ static const char* const _renderWindow =
 	"uniform ivec4 win1[160];\n"
 	"uniform vec3 circle0;\n"
 	"uniform vec3 circle1;\n"
+	"uniform bool disableInterp;\n"
 	"OUT(0) out ivec4 window;\n"
 
 	"bool crop(vec4 windowParams) {\n"
@@ -532,7 +534,7 @@ static const char* const _renderWindow =
 	"}\n"
 
 	"vec4 interpolate(vec4 top, vec4 bottom) {\n"
-	"	if (distance(top, bottom) > 40.) {\n"
+	"	if (disableInterp || distance(top, bottom) > 40.) {\n"
 	"		return top;\n"
 	"	}\n"
 	"	return vec4(mix(bottom.xy, top.xy, fract(texCoord.y)), top.zw);\n"
@@ -2111,6 +2113,7 @@ void GBAVideoGLRendererDrawWindow(struct GBAVideoGLRenderer* renderer, int y) {
 		glUniform3i(uniforms[GBA_GL_WIN_FLAGS], renderer->winN[0].control, renderer->winN[1].control, renderer->winout);
 		glUniform4iv(uniforms[GBA_GL_WIN_WIN0], GBA_VIDEO_VERTICAL_PIXELS, renderer->winNHistory[0]);
 		glUniform4iv(uniforms[GBA_GL_WIN_WIN1], GBA_VIDEO_VERTICAL_PIXELS, renderer->winNHistory[1]);
+		glUniform1i(uniforms[GBA_GL_WIN_DISABLE_INTERP], renderer->scale < 2);
 		_detectCircle(renderer, y, 0);
 		_detectCircle(renderer, y, 1);
 		glDrawArrays(GL_TRIANGLE_FAN, 0, 4);