From 1d48dd095d026ed1ae19a8f486795afd65dd3190 Mon Sep 17 00:00:00 2001
From: Gleb Mazovetskiy <glex.spb@gmail.com>
Date: Wed, 25 Aug 2021 17:42:16 +0100
Subject: [PATCH] Scale hardware cursor bilinearly

Make the hardware cursor blurry like the rest of the screen.
---
 CMakeLists.txt                      |   1 +
 Source/hwcursor.cpp                 |  12 +++-
 Source/utils/sdl_bilinear_scale.cpp | 101 ++++++++++++++++++++++++++++
 Source/utils/sdl_bilinear_scale.hpp |  19 ++++++
 4 files changed, 132 insertions(+), 1 deletion(-)
 create mode 100644 Source/utils/sdl_bilinear_scale.cpp
 create mode 100644 Source/utils/sdl_bilinear_scale.hpp

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 484400bf8..e73e09a42 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -417,6 +417,7 @@ set(libdevilutionx_SRCS
   Source/utils/file_util.cpp
   Source/utils/language.cpp
   Source/utils/paths.cpp
+  Source/utils/sdl_bilinear_scale.cpp
   Source/utils/sdl_thread.cpp
   Source/DiabloUI/art.cpp
   Source/DiabloUI/art_draw.cpp
diff --git a/Source/hwcursor.cpp b/Source/hwcursor.cpp
index 0fbd54735..d27df25a7 100644
--- a/Source/hwcursor.cpp
+++ b/Source/hwcursor.cpp
@@ -15,6 +15,7 @@
 #include "cursor.h"
 #include "engine.h"
 #include "utils/display.h"
+#include "utils/sdl_bilinear_scale.hpp"
 #include "utils/sdl_wrap.h"
 
 namespace devilution {
@@ -61,6 +62,11 @@ Point GetHotpointPosition(const SDL_Surface &surface, HotpointPosition position)
 	app_fatal("Unhandled enum value");
 }
 
+bool ShouldUseBilinearScaling()
+{
+	return sgOptions.Graphics.szScaleQuality[0] != '0';
+}
+
 bool SetHardwareCursor(SDL_Surface *surface, HotpointPosition hotpointPosition)
 {
 	SDLCursorUniquePtr newCursor;
@@ -75,7 +81,11 @@ bool SetHardwareCursor(SDL_Surface *surface, HotpointPosition hotpointPosition)
 		SDLSurfaceUniquePtr converted { SDL_ConvertSurfaceFormat(surface, SDL_PIXELFORMAT_ARGB8888, 0) };
 
 		SDLSurfaceUniquePtr scaledSurface = SDLWrap::CreateRGBSurfaceWithFormat(0, scaledSize.width, scaledSize.height, 32, SDL_PIXELFORMAT_ARGB8888);
-		SDL_BlitScaled(converted.get(), nullptr, scaledSurface.get(), nullptr);
+		if (ShouldUseBilinearScaling()) {
+			BilinearScale32(converted.get(), scaledSurface.get());
+		} else {
+			SDL_BlitScaled(converted.get(), nullptr, scaledSurface.get(), nullptr);
+		}
 		const Point hotpoint = GetHotpointPosition(*scaledSurface, hotpointPosition);
 		newCursor = SDLCursorUniquePtr { SDL_CreateColorCursor(scaledSurface.get(), hotpoint.x, hotpoint.y) };
 	}
diff --git a/Source/utils/sdl_bilinear_scale.cpp b/Source/utils/sdl_bilinear_scale.cpp
new file mode 100644
index 000000000..67d970d08
--- /dev/null
+++ b/Source/utils/sdl_bilinear_scale.cpp
@@ -0,0 +1,101 @@
+#include "utils/sdl_bilinear_scale.hpp"
+
+#include <cstdint>
+#include <memory>
+
+// Performs bilinear scaling using fixed-width integer math.
+
+namespace devilution {
+
+namespace {
+
+unsigned Frac(unsigned fixedPoint)
+{
+	return fixedPoint & 0xffff;
+}
+
+unsigned ToInt(unsigned fixedPoint)
+{
+	return fixedPoint >> 16;
+}
+
+std::unique_ptr<unsigned[]> CreateMixFactors(unsigned srcSize, unsigned dstSize)
+{
+	std::unique_ptr<unsigned[]> result { new unsigned[dstSize + 1] };
+	const auto scale = static_cast<unsigned>(65536.0 * static_cast<float>(srcSize - 1) / dstSize);
+	unsigned mix = 0;
+	for (unsigned i = 0; i <= dstSize; ++i) {
+		result[i] = mix;
+		mix = Frac(mix) + scale;
+	}
+	return result;
+};
+
+std::uint8_t MixColors(std::uint8_t first, std::uint8_t second, unsigned ratio)
+{
+	return ToInt((second - first) * ratio) + first;
+}
+
+} // namespace
+
+void BilinearScale32(SDL_Surface *src, SDL_Surface *dst)
+{
+	const std::unique_ptr<unsigned[]> mixXs = CreateMixFactors(src->w, dst->w);
+	const std::unique_ptr<unsigned[]> mixYs = CreateMixFactors(src->h, dst->h);
+
+	const unsigned dgap = dst->pitch - dst->w * 4;
+
+	auto *srcPixels = static_cast<std::uint8_t *>(src->pixels);
+	auto *dstPixels = static_cast<std::uint8_t *>(dst->pixels);
+
+	unsigned *curMixY = &mixYs[0];
+	unsigned srcY = 0;
+	for (unsigned y = 0; y < static_cast<unsigned>(dst->h); ++y) {
+		std::uint8_t *s[4] = {
+			srcPixels,                 // Self
+			srcPixels + 4,             // Right
+			srcPixels + src->pitch,    // Bottom
+			srcPixels + src->pitch + 4 // Bottom right
+		};
+
+		unsigned *curMixX = &mixXs[0];
+		unsigned srcX = 0;
+		for (unsigned x = 0; x < static_cast<unsigned>(dst->w); ++x) {
+			const unsigned mixX = Frac(*curMixX);
+			const unsigned mixY = Frac(*curMixY);
+			for (unsigned channel = 0; channel < 4; ++channel) {
+				dstPixels[channel] = MixColors(
+				    MixColors(s[0][channel], s[1][channel], mixX),
+				    MixColors(s[2][channel], s[3][channel], mixX),
+				    mixY);
+			}
+
+			++curMixX;
+			if (*curMixX > 0) {
+				unsigned step = ToInt(*curMixX);
+				srcX += step;
+				if (srcX <= static_cast<unsigned>(src->w)) {
+					step *= 4;
+					for (auto &v : s) {
+						v += step;
+					}
+				}
+			}
+
+			dstPixels += 4;
+		}
+
+		++curMixY;
+		if (*curMixY > 0) {
+			const unsigned step = ToInt(*curMixY);
+			srcY += step;
+			if (srcY < static_cast<unsigned>(src->h)) {
+				srcPixels += step * src->pitch;
+			}
+		}
+
+		dstPixels += dgap;
+	}
+}
+
+} // namespace devilution
diff --git a/Source/utils/sdl_bilinear_scale.hpp b/Source/utils/sdl_bilinear_scale.hpp
new file mode 100644
index 000000000..00ddd0e90
--- /dev/null
+++ b/Source/utils/sdl_bilinear_scale.hpp
@@ -0,0 +1,19 @@
+#pragma once
+
+#include <SDL_version.h>
+
+#if SDL_VERSION_ATLEAST(2, 0, 0)
+#include <SDL_surface.h>
+#else
+#include <SDL_video.h>
+#endif
+
+namespace devilution {
+
+/**
+ * @brief Bilinear 32-bit scaling.
+ * Requires `src` and `dst` to have the same pixel format (ARGB8888 or RGBA8888).
+ */
+void BilinearScale32(SDL_Surface *src, SDL_Surface *dst);
+
+} // namespace devilution