From e7407770cb84a61d7c519de2f21822b9d4e25d77 Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Tue, 26 Dec 2017 16:35:15 -0500
Subject: [PATCH] GB Video: Improved window implementation

---
 include/mgba/internal/gb/renderers/software.h |  2 ++
 src/gb/renderers/software.c                   | 36 +++++++++++++++++--
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/include/mgba/internal/gb/renderers/software.h b/include/mgba/internal/gb/renderers/software.h
index 038c660b8..abf437ab0 100644
--- a/include/mgba/internal/gb/renderers/software.h
+++ b/include/mgba/internal/gb/renderers/software.h
@@ -31,6 +31,8 @@ struct GBVideoSoftwareRenderer {
 	uint8_t wy;
 	uint8_t wx;
 	uint8_t currentWy;
+	int lastY;
+	bool hasWindow;
 
 	GBRegisterLCDC lcdc;
 	enum GBModel model;
diff --git a/src/gb/renderers/software.c b/src/gb/renderers/software.c
index 1a6688578..8ec3444e3 100644
--- a/src/gb/renderers/software.c
+++ b/src/gb/renderers/software.c
@@ -38,6 +38,10 @@ static void _clearScreen(struct GBVideoSoftwareRenderer* renderer) {
 	}
 }
 
+static bool _inWindow(struct GBVideoSoftwareRenderer* renderer) {
+	return GBRegisterLCDCIsWindow(renderer->lcdc) && GB_VIDEO_HORIZONTAL_PIXELS + 7 > renderer->wx;
+}
+
 void GBVideoSoftwareRendererCreate(struct GBVideoSoftwareRenderer* renderer) {
 	renderer->d.init = GBVideoSoftwareRendererInit;
 	renderer->d.deinit = GBVideoSoftwareRendererDeinit;
@@ -65,6 +69,8 @@ static void GBVideoSoftwareRendererInit(struct GBVideoRenderer* renderer, enum G
 	softwareRenderer->scx = 0;
 	softwareRenderer->wy = 0;
 	softwareRenderer->currentWy = 0;
+	softwareRenderer->lastY = 0;
+	softwareRenderer->hasWindow = false;
 	softwareRenderer->wx = 0;
 	softwareRenderer->model = model;
 }
@@ -74,11 +80,31 @@ static void GBVideoSoftwareRendererDeinit(struct GBVideoRenderer* renderer) {
 	UNUSED(softwareRenderer);
 }
 
+static void GBVideoSoftwareRendererUpdateWindow(struct GBVideoSoftwareRenderer* renderer, bool before, bool after) {
+	if (renderer->lastY >= GB_VIDEO_VERTICAL_PIXELS || after == before) {
+		return;
+	}
+	if (renderer->lastY >= renderer->wy) {
+		if (!after) {
+			renderer->currentWy -= renderer->lastY;
+			renderer->hasWindow = true;
+		} else {
+			if (!renderer->hasWindow) {
+				renderer->currentWy = renderer->lastY + 1 - renderer->wy;
+			} else {
+				renderer->currentWy += renderer->lastY;
+			}
+		}
+	}
+}
+
 static uint8_t GBVideoSoftwareRendererWriteVideoRegister(struct GBVideoRenderer* renderer, uint16_t address, uint8_t value) {
 	struct GBVideoSoftwareRenderer* softwareRenderer = (struct GBVideoSoftwareRenderer*) renderer;
+	bool wasWindow = _inWindow(softwareRenderer);
 	switch (address) {
 	case REG_LCDC:
 		softwareRenderer->lcdc = value;
+		GBVideoSoftwareRendererUpdateWindow(softwareRenderer, wasWindow, _inWindow(softwareRenderer));
 		break;
 	case REG_SCY:
 		softwareRenderer->scy = value;
@@ -88,9 +114,11 @@ static uint8_t GBVideoSoftwareRendererWriteVideoRegister(struct GBVideoRenderer*
 		break;
 	case REG_WY:
 		softwareRenderer->wy = value;
+		GBVideoSoftwareRendererUpdateWindow(softwareRenderer, wasWindow, _inWindow(softwareRenderer));
 		break;
 	case REG_WX:
 		softwareRenderer->wx = value;
+		GBVideoSoftwareRendererUpdateWindow(softwareRenderer, wasWindow, _inWindow(softwareRenderer));
 		break;
 	}
 	return value;
@@ -134,6 +162,7 @@ static void GBVideoSoftwareRendererWriteOAM(struct GBVideoRenderer* renderer, ui
 
 static void GBVideoSoftwareRendererDrawRange(struct GBVideoRenderer* renderer, int startX, int endX, int y, struct GBObj* obj, size_t oamMax) {
 	struct GBVideoSoftwareRenderer* softwareRenderer = (struct GBVideoSoftwareRenderer*) renderer;
+	softwareRenderer->lastY = y;
 	uint8_t* maps = &softwareRenderer->d.vram[GB_BASE_MAP];
 	if (GBRegisterLCDCIsTileMap(softwareRenderer->lcdc)) {
 		maps += GB_SIZE_MAP;
@@ -142,7 +171,8 @@ static void GBVideoSoftwareRendererDrawRange(struct GBVideoRenderer* renderer, i
 		memset(&softwareRenderer->row[startX], 0, endX - startX);
 	}
 	if (GBRegisterLCDCIsBgEnable(softwareRenderer->lcdc) || softwareRenderer->model >= GB_MODEL_CGB) {
-		if (GBRegisterLCDCIsWindow(softwareRenderer->lcdc) && softwareRenderer->wy <= y && endX >= softwareRenderer->wx - 7) {
+		int wy = softwareRenderer->wy + softwareRenderer->currentWy;
+		if (GBRegisterLCDCIsWindow(softwareRenderer->lcdc) && wy <= y && endX >= softwareRenderer->wx - 7) {
 			if (softwareRenderer->wx - 7 > 0 && !softwareRenderer->d.disableBG) {
 				GBVideoSoftwareRendererDrawBackground(softwareRenderer, maps, startX, softwareRenderer->wx - 7, softwareRenderer->scx, softwareRenderer->scy + y);
 			}
@@ -152,7 +182,7 @@ static void GBVideoSoftwareRendererDrawRange(struct GBVideoRenderer* renderer, i
 				maps += GB_SIZE_MAP;
 			}
 			if (!softwareRenderer->d.disableWIN) {
-				GBVideoSoftwareRendererDrawBackground(softwareRenderer, maps, softwareRenderer->wx - 7, endX, 7 - softwareRenderer->wx, softwareRenderer->currentWy);
+				GBVideoSoftwareRendererDrawBackground(softwareRenderer, maps, softwareRenderer->wx - 7, endX, 7 - softwareRenderer->wx, y - wy);
 			}
 		} else if (!softwareRenderer->d.disableBG) {
 			GBVideoSoftwareRendererDrawBackground(softwareRenderer, maps, startX, endX, softwareRenderer->scx, softwareRenderer->scy + y);
@@ -201,7 +231,9 @@ static void GBVideoSoftwareRendererFinishFrame(struct GBVideoRenderer* renderer)
 	if (!GBRegisterLCDCIsEnable(softwareRenderer->lcdc)) {
 		_clearScreen(softwareRenderer);
 	}
+	softwareRenderer->lastY = GB_VIDEO_VERTICAL_PIXELS;
 	softwareRenderer->currentWy = 0;
+	softwareRenderer->hasWindow = false;
 }
 
 static void GBVideoSoftwareRendererDrawBackground(struct GBVideoSoftwareRenderer* renderer, uint8_t* maps, int startX, int endX, int sx, int sy) {