GH-1197 add console log color adaptation

rainbow library was part of KDE - KGuiAddons

CMakeLists.txt

@@ -112,6 +112,10 @@ include_directories(${XZ_INCLUDE_DIR})
 add_subdirectory(depends/pack200)
 include_directories(${PACK200_INCLUDE_DIR})
 
+# Add color thingy
+add_subdirectory(depends/rainbow)
+include_directories(${RAINBOW_INCLUDE_DIR})
+
 ######## MultiMC Libs ########
 
 # Add the util library.

application/CMakeLists.txt

@@ -129,6 +129,8 @@ SET(MULTIMC_SOURCES
 	InstanceProxyModel.cpp
 	VersionProxyModel.h
 	VersionProxyModel.cpp
+	Colors.h
+	Colors.cpp
 
 	# GUI - windows
 	MainWindow.h
@@ -325,7 +327,6 @@ else()
 	list(APPEND MULTIMC_SOURCES Platform_Other.cpp)
 endif()
 
-
 # Link additional libraries
 if(WIN32)
 	set(MultiMC_LINK_ADDITIONAL_LIBS ${MultiMC_LINK_ADDITIONAL_LIBS} Qt5::WinMain)
@@ -341,8 +342,8 @@ qt5_add_resources(MULTIMC_RESOURCES ${MULTIMC_QRCS})
 add_executable(MultiMC MACOSX_BUNDLE WIN32 ${MULTIMC_SOURCES} ${MULTIMC_UI} ${MULTIMC_RESOURCES} ${MULTIMC_RCS})
 target_link_libraries(MultiMC MultiMC_logic xz-embedded unpack200 iconfix libUtil LogicalGui
 	${QUAZIP_LIBRARIES} Qt5::Core Qt5::Xml Qt5::Widgets Qt5::Network Qt5::Concurrent
-	hoedown
-		${MultiMC_LINK_ADDITIONAL_LIBS})
+		hoedown rainbow
+			${MultiMC_LINK_ADDITIONAL_LIBS})
 
 ################################ INSTALLATION AND PACKAGING ################################
 

application/Colors.cpp

@@ -0,0 +1,26 @@
+#include "Colors.h"
+
+/**
+ * Blend the color with the front color, adapting to the back color
+ */
+QColor Color::blend(QColor front, QColor back, QColor color, uchar ratio)
+{
+	Q_ASSERT(front.isValid());
+	Q_ASSERT(back.isValid());
+	if (Rainbow::luma(front) > Rainbow::luma(back))
+	{
+		// for dark color schemes, produce a fitting color first
+		color = Rainbow::tint(front, color, 0.5);
+	}
+	// adapt contrast
+	return Rainbow::mix(front, color, float(ratio) / float(0xff));
+}
+
+/**
+ * Blend the color with the back color
+ */
+QColor Color::blendBackground(QColor back, QColor color, uchar ratio)
+{
+	// adapt contrast
+	return Rainbow::mix(back, color, float(ratio) / float(0xff));
+}

application/Colors.h

@@ -0,0 +1,15 @@
+#pragma once
+#include <QtGui/QColor>
+#include <rainbow.h>
+namespace Color
+{
+/**
+ * Blend the color with the front color, adapting to the back color
+ */
+QColor blend(QColor front, QColor back, QColor color, uchar ratio);
+
+/**
+ * Blend the color with the back color
+ */
+QColor blendBackground(QColor back, QColor color, uchar ratio);
+}

application/pages/LogPage.cpp

@@ -10,6 +10,7 @@
 #include "launch/LaunchTask.h"
 #include <settings/Setting.h>
 #include "GuiUtil.h"
+#include <Colors.h>
 
 LogPage::LogPage(std::shared_ptr<LaunchTask> proc, QWidget *parent)
 	: QWidget(parent), ui(new Ui::LogPage), m_process(proc)
@@ -203,31 +204,38 @@ void LogPage::write(QString data, MessageLevel::Enum mode)
 	QListIterator<QString> iter(filtered);
 	QTextCharFormat format(*defaultFormat);
 
+	auto origForeground = ui->text->palette().color(ui->text->foregroundRole());
+	auto origBackground = ui->text->palette().color(ui->text->backgroundRole());
+	auto foreground = [&](QColor foreColor)
+	{
+		format.setForeground(Color::blend(origForeground, origBackground, foreColor, 255));
+	};
 	switch(mode)
 	{
 		case MessageLevel::MultiMC:
 		{
-			format.setForeground(QColor("blue"));
+			foreground(QColor("purple"));
 			break;
 		}
 		case MessageLevel::Debug:
 		{
-			format.setForeground(QColor("green"));
+			foreground(QColor("green"));
 			break;
 		}
 		case MessageLevel::Warning:
 		{
-			format.setForeground(QColor("orange"));
+			foreground(QColor("orange"));
 			break;
 		}
 		case MessageLevel::Error:
 		{
-			format.setForeground(QColor("red"));
+			foreground(QColor("red"));
 			break;
 		}
 		case MessageLevel::Fatal:
 		{
-			format.setForeground(QColor("red"));
+			origBackground = QColor("black");
+			foreground(QColor("red"));
 			format.setBackground(QColor("black"));
 			break;
 		}
@@ -235,7 +243,7 @@ void LogPage::write(QString data, MessageLevel::Enum mode)
 		case MessageLevel::Message:
 		default:
 		{
-			// do nothing, keep original
+			foreground(QColor("black"));
 		}
 	}
 

depends/rainbow/CMakeLists.txt

@@ -0,0 +1,20 @@
+cmake_minimum_required(VERSION 2.8.11)
+project(rainbow)
+
+find_package(Qt5Core REQUIRED QUIET)
+find_package(Qt5Gui REQUIRED QUIET)
+
+include_directories(${Qt5Core_INCLUDE_DIRS})
+include_directories(${Qt5Gui_INCLUDE_DIRS})
+
+set(RAINBOW_SOURCES
+include/rainbow_config.h
+include/rainbow.h
+src/rainbow.cpp
+)
+
+add_definitions(-DRAINBOW_LIBRARY)
+set(RAINBOW_INCLUDE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/include" PARENT_SCOPE)
+add_library(rainbow SHARED ${RAINBOW_SOURCES})
+
+qt5_use_modules(rainbow Core Gui)

depends/rainbow/include/rainbow.h

@@ -0,0 +1,160 @@
+/* This was part of the KDE project - see KGuiAddons
+ * Copyright (C) 2007 Matthew Woehlke <mw_triad@users.sourceforge.net>
+ * Copyright (C) 2007 Olaf Schmidt <ojschmidt@kde.org>
+ * Copyright (C) 2007 Thomas Zander <zander@kde.org>
+ * Copyright (C) 2007 Zack Rusin <zack@kde.org>
+ * Copyright (C) 2015 Petr Mrazek <peterix@gmail.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public License
+ * along with this library; see the file COPYING.LIB.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#pragma once
+
+#include "rainbow_config.h"
+
+#include <QPainter>
+class QColor;
+
+/**
+ * A set of methods used to work with colors.
+ */
+namespace Rainbow
+{
+/**
+ * Calculate the luma of a color. Luma is weighted sum of gamma-adjusted
+ * R'G'B' components of a color. The result is similar to qGray. The range
+ * is from 0.0 (black) to 1.0 (white).
+ *
+ * Rainbow::darken(), Rainbow::lighten() and Rainbow::shade()
+ * operate on the luma of a color.
+ *
+ * @see http://en.wikipedia.org/wiki/Luma_(video)
+ */
+RAINBOW_EXPORT qreal luma(const QColor &);
+
+/**
+ * Calculate hue, chroma and luma of a color in one call.
+ * @since 5.0
+ */
+RAINBOW_EXPORT void getHcy(const QColor &, qreal *hue, qreal *chroma, qreal *luma,
+						   qreal *alpha = 0);
+
+/**
+ * Calculate the contrast ratio between two colors, according to the
+ * W3C/WCAG2.0 algorithm, (Lmax + 0.05)/(Lmin + 0.05), where Lmax and Lmin
+ * are the luma values of the lighter color and the darker color,
+ * respectively.
+ *
+ * A contrast ration of 5:1 (result == 5.0) is the minimum for "normal"
+ * text to be considered readable (large text can go as low as 3:1). The
+ * ratio ranges from 1:1 (result == 1.0) to 21:1 (result == 21.0).
+ *
+ * @see Rainbow::luma
+ */
+RAINBOW_EXPORT qreal contrastRatio(const QColor &, const QColor &);
+
+/**
+ * Adjust the luma of a color by changing its distance from white.
+ *
+ * @li amount == 1.0 gives white
+ * @li amount == 0.5 results in a color whose luma is halfway between 1.0
+ * and that of the original color
+ * @li amount == 0.0 gives the original color
+ * @li amount == -1.0 gives a color that is 'twice as far from white' as
+ * the original color, that is luma(result) == 1.0 - 2*(1.0 - luma(color))
+ *
+ * @param amount factor by which to adjust the luma component of the color
+ * @param chromaInverseGain (optional) factor by which to adjust the chroma
+ * component of the color; 1.0 means no change, 0.0 maximizes chroma
+ * @see Rainbow::shade
+ */
+RAINBOW_EXPORT QColor
+lighten(const QColor &, qreal amount = 0.5, qreal chromaInverseGain = 1.0);
+
+/**
+ * Adjust the luma of a color by changing its distance from black.
+ *
+ * @li amount == 1.0 gives black
+ * @li amount == 0.5 results in a color whose luma is halfway between 0.0
+ * and that of the original color
+ * @li amount == 0.0 gives the original color
+ * @li amount == -1.0 gives a color that is 'twice as far from black' as
+ * the original color, that is luma(result) == 2*luma(color)
+ *
+ * @param amount factor by which to adjust the luma component of the color
+ * @param chromaGain (optional) factor by which to adjust the chroma
+ * component of the color; 1.0 means no change, 0.0 minimizes chroma
+ * @see Rainbow::shade
+ */
+RAINBOW_EXPORT QColor darken(const QColor &, qreal amount = 0.5, qreal chromaGain = 1.0);
+
+/**
+ * Adjust the luma and chroma components of a color. The amount is added
+ * to the corresponding component.
+ *
+ * @param lumaAmount amount by which to adjust the luma component of the
+ * color; 0.0 results in no change, -1.0 turns anything black, 1.0 turns
+ * anything white
+ * @param chromaAmount (optional) amount by which to adjust the chroma
+ * component of the color; 0.0 results in no change, -1.0 minimizes chroma,
+ * 1.0 maximizes chroma
+ * @see Rainbow::luma
+ */
+RAINBOW_EXPORT QColor shade(const QColor &, qreal lumaAmount, qreal chromaAmount = 0.0);
+
+/**
+ * Create a new color by tinting one color with another. This function is
+ * meant for creating additional colors withings the same class (background,
+ * foreground) from colors in a different class. Therefore when @p amount
+ * is low, the luma of @p base is mostly preserved, while the hue and
+ * chroma of @p color is mostly inherited.
+ *
+ * @param base color to be tinted
+ * @param color color with which to tint
+ * @param amount how strongly to tint the base; 0.0 gives @p base,
+ * 1.0 gives @p color
+ */
+RAINBOW_EXPORT QColor tint(const QColor &base, const QColor &color, qreal amount = 0.3);
+
+/**
+ * Blend two colors into a new color by linear combination.
+ * @code
+	QColor lighter = Rainbow::mix(myColor, Qt::white)
+ * @endcode
+ * @param c1 first color.
+ * @param c2 second color.
+ * @param bias weight to be used for the mix. @p bias <= 0 gives @p c1,
+ * @p bias >= 1 gives @p c2. @p bias == 0.5 gives a 50% blend of @p c1
+ * and @p c2.
+ */
+RAINBOW_EXPORT QColor mix(const QColor &c1, const QColor &c2, qreal bias = 0.5);
+
+/**
+ * Blend two colors into a new color by painting the second color over the
+ * first using the specified composition mode.
+ * @code
+	QColor white(Qt::white);
+	white.setAlphaF(0.5);
+	QColor lighter = Rainbow::overlayColors(myColor, white);
+   @endcode
+ * @param base the base color (alpha channel is ignored).
+ * @param paint the color to be overlayed onto the base color.
+ * @param comp the CompositionMode used to do the blending.
+ */
+RAINBOW_EXPORT QColor
+overlayColors(const QColor &base, const QColor &paint,
+			  QPainter::CompositionMode comp = QPainter::CompositionMode_SourceOver);
+}

depends/rainbow/include/rainbow_config.h

@@ -0,0 +1,22 @@
+/* Copyright 2013-2015 MultiMC Contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <QtCore/QtGlobal>
+
+#ifdef RAINBOW_LIBRARY
+#define RAINBOW_EXPORT Q_DECL_EXPORT
+#else
+#define RAINBOW_EXPORT Q_DECL_IMPORT
+#endif

depends/rainbow/src/rainbow.cpp

@@ -0,0 +1,365 @@
+/* This was part of the KDE project - see KGuiAddons
+ * Copyright (C) 2007 Matthew Woehlke <mw_triad@users.sourceforge.net>
+ * Copyright (C) 2007 Olaf Schmidt <ojschmidt@kde.org>
+ * Copyright (C) 2007 Thomas Zander <zander@kde.org>
+ * Copyright (C) 2007 Zack Rusin <zack@kde.org>
+ * Copyright (C) 2015 Petr Mrazek <peterix@gmail.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public License
+ * along with this library; see the file COPYING.LIB.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#include "../include/rainbow.h"
+
+#include <QColor>
+#include <QImage>
+#include <QtNumeric> // qIsNaN
+
+#include <math.h>
+
+//BEGIN internal helper functions
+
+static inline qreal wrap(qreal a, qreal d = 1.0)
+{
+	qreal r = fmod(a, d);
+	return (r < 0.0 ? d + r : (r > 0.0 ? r : 0.0));
+}
+
+// normalize: like qBound(a, 0.0, 1.0) but without needing the args and with
+// "safer" behavior on NaN (isnan(a) -> return 0.0)
+static inline qreal normalize(qreal a)
+{
+    return (a < 1.0 ? (a > 0.0 ? a : 0.0) : 1.0);
+}
+
+
+///////////////////////////////////////////////////////////////////////////////
+// HCY color space
+
+#define HCY_REC 709 // use 709 for now
+#if HCY_REC == 601
+static const qreal yc[3] = {0.299, 0.587, 0.114};
+#elif HCY_REC == 709
+static const qreal yc[3] = {0.2126, 0.7152, 0.0722};
+#else // use Qt values
+static const qreal yc[3] = {0.34375, 0.5, 0.15625};
+#endif
+
+class KHCY
+{
+public:
+	explicit KHCY(const QColor &color)
+	{
+		qreal r = gamma(color.redF());
+		qreal g = gamma(color.greenF());
+		qreal b = gamma(color.blueF());
+		a = color.alphaF();
+
+		// luma component
+		y = lumag(r, g, b);
+
+		// hue component
+		qreal p = qMax(qMax(r, g), b);
+		qreal n = qMin(qMin(r, g), b);
+		qreal d = 6.0 * (p - n);
+		if (n == p)
+		{
+			h = 0.0;
+		}
+		else if (r == p)
+		{
+			h = ((g - b) / d);
+		}
+		else if (g == p)
+		{
+			h = ((b - r) / d) + (1.0 / 3.0);
+		}
+		else
+		{
+			h = ((r - g) / d) + (2.0 / 3.0);
+		}
+
+		// chroma component
+		if (r == g && g == b)
+		{
+			c = 0.0;
+		}
+		else
+		{
+			c = qMax((y - n) / y, (p - y) / (1 - y));
+		}
+	}
+	explicit KHCY(qreal h_, qreal c_, qreal y_, qreal a_ = 1.0)
+	{
+		h = h_;
+		c = c_;
+		y = y_;
+		a = a_;
+	}
+
+	QColor qColor() const
+	{
+		// start with sane component values
+		qreal _h = wrap(h);
+		qreal _c = normalize(c);
+		qreal _y = normalize(y);
+
+		// calculate some needed variables
+		qreal _hs = _h * 6.0, th, tm;
+		if (_hs < 1.0)
+		{
+			th = _hs;
+			tm = yc[0] + yc[1] * th;
+		}
+		else if (_hs < 2.0)
+		{
+			th = 2.0 - _hs;
+			tm = yc[1] + yc[0] * th;
+		}
+		else if (_hs < 3.0)
+		{
+			th = _hs - 2.0;
+			tm = yc[1] + yc[2] * th;
+		}
+		else if (_hs < 4.0)
+		{
+			th = 4.0 - _hs;
+			tm = yc[2] + yc[1] * th;
+		}
+		else if (_hs < 5.0)
+		{
+			th = _hs - 4.0;
+			tm = yc[2] + yc[0] * th;
+		}
+		else
+		{
+			th = 6.0 - _hs;
+			tm = yc[0] + yc[2] * th;
+		}
+
+		// calculate RGB channels in sorted order
+		qreal tn, to, tp;
+		if (tm >= _y)
+		{
+			tp = _y + _y * _c * (1.0 - tm) / tm;
+			to = _y + _y * _c * (th - tm) / tm;
+			tn = _y - (_y * _c);
+		}
+		else
+		{
+			tp = _y + (1.0 - _y) * _c;
+			to = _y + (1.0 - _y) * _c * (th - tm) / (1.0 - tm);
+			tn = _y - (1.0 - _y) * _c * tm / (1.0 - tm);
+		}
+
+		// return RGB channels in appropriate order
+		if (_hs < 1.0)
+		{
+			return QColor::fromRgbF(igamma(tp), igamma(to), igamma(tn), a);
+		}
+		else if (_hs < 2.0)
+		{
+			return QColor::fromRgbF(igamma(to), igamma(tp), igamma(tn), a);
+		}
+		else if (_hs < 3.0)
+		{
+			return QColor::fromRgbF(igamma(tn), igamma(tp), igamma(to), a);
+		}
+		else if (_hs < 4.0)
+		{
+			return QColor::fromRgbF(igamma(tn), igamma(to), igamma(tp), a);
+		}
+		else if (_hs < 5.0)
+		{
+			return QColor::fromRgbF(igamma(to), igamma(tn), igamma(tp), a);
+		}
+		else
+		{
+			return QColor::fromRgbF(igamma(tp), igamma(tn), igamma(to), a);
+		}
+	}
+
+	qreal h, c, y, a;
+	static qreal luma(const QColor &color)
+	{
+		return lumag(gamma(color.redF()), gamma(color.greenF()), gamma(color.blueF()));
+	}
+
+private:
+	static qreal gamma(qreal n)
+	{
+		return pow(normalize(n), 2.2);
+	}
+	static qreal igamma(qreal n)
+	{
+		return pow(normalize(n), 1.0 / 2.2);
+	}
+	static qreal lumag(qreal r, qreal g, qreal b)
+	{
+		return r * yc[0] + g * yc[1] + b * yc[2];
+	}
+};
+
+static inline qreal mixQreal(qreal a, qreal b, qreal bias)
+{
+	return a + (b - a) * bias;
+}
+//END internal helper functions
+
+qreal Rainbow::luma(const QColor &color)
+{
+	return KHCY::luma(color);
+}
+
+void Rainbow::getHcy(const QColor &color, qreal *h, qreal *c, qreal *y, qreal *a)
+{
+	if (!c || !h || !y)
+	{
+		return;
+	}
+	KHCY khcy(color);
+	*c = khcy.c;
+	*h = khcy.h;
+	*y = khcy.y;
+	if (a)
+	{
+		*a = khcy.a;
+	}
+}
+
+static qreal contrastRatioForLuma(qreal y1, qreal y2)
+{
+	if (y1 > y2)
+	{
+		return (y1 + 0.05) / (y2 + 0.05);
+	}
+	else
+	{
+		return (y2 + 0.05) / (y1 + 0.05);
+	}
+}
+
+qreal Rainbow::contrastRatio(const QColor &c1, const QColor &c2)
+{
+	return contrastRatioForLuma(luma(c1), luma(c2));
+}
+
+QColor Rainbow::lighten(const QColor &color, qreal ky, qreal kc)
+{
+	KHCY c(color);
+	c.y = 1.0 - normalize((1.0 - c.y) * (1.0 - ky));
+	c.c = 1.0 - normalize((1.0 - c.c) * kc);
+	return c.qColor();
+}
+
+QColor Rainbow::darken(const QColor &color, qreal ky, qreal kc)
+{
+	KHCY c(color);
+	c.y = normalize(c.y * (1.0 - ky));
+	c.c = normalize(c.c * kc);
+	return c.qColor();
+}
+
+QColor Rainbow::shade(const QColor &color, qreal ky, qreal kc)
+{
+	KHCY c(color);
+	c.y = normalize(c.y + ky);
+	c.c = normalize(c.c + kc);
+	return c.qColor();
+}
+
+static QColor tintHelper(const QColor &base, qreal baseLuma, const QColor &color, qreal amount)
+{
+	KHCY result(Rainbow::mix(base, color, pow(amount, 0.3)));
+	result.y = mixQreal(baseLuma, result.y, amount);
+
+	return result.qColor();
+}
+
+QColor Rainbow::tint(const QColor &base, const QColor &color, qreal amount)
+{
+	if (amount <= 0.0)
+	{
+		return base;
+	}
+	if (amount >= 1.0)
+	{
+		return color;
+	}
+	if (qIsNaN(amount))
+	{
+		return base;
+	}
+
+	qreal baseLuma = luma(base); // cache value because luma call is expensive
+	double ri = contrastRatioForLuma(baseLuma, luma(color));
+	double rg = 1.0 + ((ri + 1.0) * amount * amount * amount);
+	double u = 1.0, l = 0.0;
+	QColor result;
+	for (int i = 12; i; --i)
+	{
+		double a = 0.5 * (l + u);
+		result = tintHelper(base, baseLuma, color, a);
+		double ra = contrastRatioForLuma(baseLuma, luma(result));
+		if (ra > rg)
+		{
+			u = a;
+		}
+		else
+		{
+			l = a;
+		}
+	}
+	return result;
+}
+
+QColor Rainbow::mix(const QColor &c1, const QColor &c2, qreal bias)
+{
+	if (bias <= 0.0)
+	{
+		return c1;
+	}
+	if (bias >= 1.0)
+	{
+		return c2;
+	}
+	if (qIsNaN(bias))
+	{
+		return c1;
+	}
+
+	qreal r = mixQreal(c1.redF(), c2.redF(), bias);
+	qreal g = mixQreal(c1.greenF(), c2.greenF(), bias);
+	qreal b = mixQreal(c1.blueF(), c2.blueF(), bias);
+	qreal a = mixQreal(c1.alphaF(), c2.alphaF(), bias);
+
+	return QColor::fromRgbF(r, g, b, a);
+}
+
+QColor Rainbow::overlayColors(const QColor &base, const QColor &paint,
+							  QPainter::CompositionMode comp)
+{
+	// This isn't the fastest way, but should be "fast enough".
+	// It's also the only safe way to use QPainter::CompositionMode
+	QImage img(1, 1, QImage::Format_ARGB32_Premultiplied);
+	QPainter p(&img);
+	QColor start = base;
+	start.setAlpha(255); // opaque
+	p.fillRect(0, 0, 1, 1, start);
+	p.setCompositionMode(comp);
+	p.fillRect(0, 0, 1, 1, paint);
+	p.end();
+	return img.pixel(0, 0);
+}