From 982260d94ec8de51e3887e7b3d8d213cd0316d06 Mon Sep 17 00:00:00 2001
From: Gleb Mazovetskiy <glex.spb@gmail.com>
Date: Wed, 16 Jun 2021 01:20:09 +0100
Subject: [PATCH] Clip control.cpp draw calls

No longer crashes there when running at a resolution smaller than
640x480
---
 Source/control.cpp | 27 +++++----------------------
 Source/engine.cpp  | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 Source/engine.h    | 34 ++++++++++++++++++++++++++++++++++
 3 files changed, 85 insertions(+), 22 deletions(-)

diff --git a/Source/control.cpp b/Source/control.cpp
index 81b542379..ca7fcd673 100644
--- a/Source/control.cpp
+++ b/Source/control.cpp
@@ -27,6 +27,7 @@
 #include "towners.h"
 #include "trigs.h"
 #include "utils/language.h"
+#include "utils/sdl_geometry.h"
 
 namespace devilution {
 namespace {
@@ -545,12 +546,7 @@ void ClearPanel()
 
 void DrawPanelBox(const CelOutputBuffer &out, SDL_Rect srcRect, Point targetPosition)
 {
-	const BYTE *src = pBtmBuff.at(srcRect.x, srcRect.y);
-	BYTE *dst = &out[targetPosition];
-
-	for (int hgt = srcRect.h; hgt != 0; hgt--, src += pBtmBuff.pitch(), dst += out.pitch()) {
-		memcpy(dst, src, srcRect.w);
-	}
+	out.BlitFrom(pBtmBuff, srcRect, targetPosition);
 }
 
 /**
@@ -565,11 +561,7 @@ void DrawPanelBox(const CelOutputBuffer &out, SDL_Rect srcRect, Point targetPosi
  */
 static void DrawFlaskTop(const CelOutputBuffer &out, Point position, const CelOutputBuffer &celBuf, int y0, int y1)
 {
-	const BYTE *src = celBuf.at(0, y0);
-	BYTE *dst = &out[position];
-
-	for (int h = y1 - y0; h != 0; --h, src += celBuf.pitch(), dst += out.pitch())
-		memcpy(dst, src, celBuf.w());
+	out.BlitFrom(celBuf, SDL_Rect { 0, static_cast<decltype(SDL_Rect {}.y)>(y0), celBuf.w(), y1 - y0 }, position);
 }
 
 /**
@@ -584,17 +576,8 @@ static void DrawFlaskTop(const CelOutputBuffer &out, Point position, const CelOu
  */
 static void DrawFlask(const CelOutputBuffer &out, const CelOutputBuffer &celBuf, Point sourcePosition, Point targetPosition, int h)
 {
-	const BYTE *src = &celBuf[sourcePosition];
-	BYTE *dst = &out[targetPosition];
-
-	for (int hgt = h; hgt != 0; hgt--, src += celBuf.pitch() - 59, dst += out.pitch() - 59) {
-		for (int wdt = 59; wdt != 0; wdt--) {
-			if (*src != 0)
-				*dst = *src;
-			src++;
-			dst++;
-		}
-	}
+	constexpr int FlaskWidth = 59;
+	out.BlitFromSkipColorIndexZero(celBuf, MakeSdlRect(sourcePosition.x, sourcePosition.y, FlaskWidth, h), targetPosition);
 }
 
 void DrawLifeFlask(const CelOutputBuffer &out)
diff --git a/Source/engine.cpp b/Source/engine.cpp
index 10b19048f..bf4e82113 100644
--- a/Source/engine.cpp
+++ b/Source/engine.cpp
@@ -36,6 +36,52 @@ const uint32_t RndInc = 1;
  */
 const uint32_t RndMult = 0x015A4E35;
 
+namespace {
+
+template <bool SkipColorIndexZero>
+void BufferBlit(const CelOutputBuffer &src, SDL_Rect srcRect, const CelOutputBuffer &dst, Point dstPosition)
+{
+	// We do not use `SDL_BlitSurface` here because the palettes may be different objects
+	// and SDL would attempt to map them.
+
+	dst.Clip(&srcRect, &dstPosition);
+	if (srcRect.w <= 0 || srcRect.h <= 0)
+		return;
+
+	const std::uint8_t *srcBuf = src.at(srcRect.x, srcRect.y);
+	const auto srcPitch = src.pitch();
+	std::uint8_t *dstBuf = &dst[dstPosition];
+	const auto dstPitch = dst.pitch();
+
+	for (unsigned h = srcRect.h; h != 0; --h) {
+		if (SkipColorIndexZero) {
+			for (unsigned w = srcRect.w; w != 0; --w) {
+				if (*srcBuf != 0)
+					*dstBuf = *srcBuf;
+				++srcBuf, ++dstBuf;
+			}
+			srcBuf += srcPitch - srcRect.w;
+			dstBuf += dstPitch - srcRect.w;
+		} else {
+			std::memcpy(dstBuf, srcBuf, srcRect.w);
+			srcBuf += srcPitch;
+			dstBuf += dstPitch;
+		}
+	}
+}
+
+} // namespace
+
+void CelOutputBuffer::BlitFrom(const CelOutputBuffer &src, SDL_Rect srcRect, Point targetPosition) const
+{
+	BufferBlit</*SkipColorIndexZero=*/false>(src, srcRect, *this, targetPosition);
+}
+
+void CelOutputBuffer::BlitFromSkipColorIndexZero(const CelOutputBuffer &src, SDL_Rect srcRect, Point targetPosition) const
+{
+	BufferBlit</*SkipColorIndexZero=*/true>(src, srcRect, *this, targetPosition);
+}
+
 CelSprite LoadCel(const char *pszName, int width)
 {
 	return CelSprite(LoadFileInMem(pszName), width);
diff --git a/Source/engine.h b/Source/engine.h
index 56374aab7..fcdff3b57 100644
--- a/Source/engine.h
+++ b/Source/engine.h
@@ -432,6 +432,40 @@ struct CelOutputBuffer {
 		subregion.h = h;
 		return CelOutputBuffer(surface, subregion);
 	}
+
+	/**
+	 * @brief Clips srcRect and targetPosition to this output buffer.
+	 */
+	void Clip(SDL_Rect *srcRect, Point *targetPosition) const
+	{
+		if (targetPosition->x < 0) {
+			srcRect->x -= targetPosition->x;
+			srcRect->w += targetPosition->x;
+			targetPosition->x = 0;
+		}
+		if (targetPosition->y < 0) {
+			srcRect->y -= targetPosition->y;
+			srcRect->h += targetPosition->y;
+			targetPosition->y = 0;
+		}
+		if (targetPosition->x + srcRect->w > region.w) {
+			srcRect->w = region.w - targetPosition->x;
+		}
+		if (targetPosition->y + srcRect->h > region.h) {
+			srcRect->h = region.h - targetPosition->y;
+		}
+	}
+
+	/**
+	 * @brief Copies the `srcRect` portion of the given buffer to this buffer at `targetPosition`.
+	 */
+	void BlitFrom(const CelOutputBuffer &src, SDL_Rect srcRect, Point targetPosition) const;
+
+	/**
+	 * @brief Copies the `srcRect` portion of the given buffer to this buffer at `targetPosition`.
+	 * Source pixels with index 0 are not copied.
+	 */
+	void BlitFromSkipColorIndexZero(const CelOutputBuffer &src, SDL_Rect srcRect, Point targetPosition) const;
 };
 
 /**