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WindowServer: Support windows with alpha channels. And per-WSWindow opacity.

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This patch also adds a Format concept to GraphicsBitmap. For now there are
only two formats: RGB32 and RGBA32. Windows with alpha channel have their
backing stores created in the RGBA32 format.

Use this to make Terminal windows semi-transparent for that comfy rice look.
There is one problem here, in that window compositing overdraw incurs
multiple passes of blending of the same pixels. This leads to a mismatch in
opacity which is obviously not good. I will work on this in a later patch.

The alpha blending is currently straight C++. It should be relatively easy
to optimize this using SSE instructions.

For now I'm just happy with the cute effect. :^)
This commit is contained in:
Andreas Kling 2019-02-19 01:42:53 +01:00
parent d4973842c9
commit 9b71307d49
25 changed files with 244 additions and 71 deletions
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38
SharedGraphics/Color.h
View file

@ -26,26 +26,48 @@ public:
Color() { }
Color(NamedColor);
Color(byte r, byte g, byte b) : m_value((r << 16) | (g << 8) | b) { }
Color(RGBA32 rgba) : m_value(rgba) { }
Color(byte r, byte g, byte b) : m_value(0xff000000 | (r << 16) | (g << 8) | b) { }
Color(byte r, byte g, byte b, byte a) : m_value((a << 24) | (r << 16) | (g << 8) | b) { }
static Color from_rgb(unsigned rgb) { return Color(rgb | 0xff000000); }
static Color from_rgba(unsigned rgba) { return Color(rgba); }
byte red() const { return (m_value >> 16) & 0xff; }
byte green() const { return (m_value >> 8) & 0xff; }
byte blue() const { return m_value & 0xff; }
byte alpha() const { return (m_value >> 24) & 0xff; }
Color blend(Color source) const
void set_alpha(byte value)
{
RGBA32 redblue1 = ((0x100u - source.alpha()) * (m_value & 0xff00ff)) >> 8;
RGBA32 redblue2 = (source.alpha() * (source.m_value & 0xff00ff)) >> 8;
RGBA32 green1 = ((0x100u - source.alpha()) * (m_value & 0x00ff00)) >> 8;
RGBA32 green2 = (source.alpha() * (source.m_value & 0x00ff00)) >> 8;
return Color(((redblue1 | redblue2) & 0xff00ff) + ((green1 | green2) & 0x00ff00));
m_value &= 0x00ffffff;
m_value |= value << 24;
}
Color with_alpha(byte alpha)
{
return Color((m_value & 0x00ffffff) | alpha << 24);
}
Color blend(Color source) const
{
if (!alpha() || source.alpha() == 255)
return source;
if (!source.alpha())
return *this;
int d = 255 * (alpha() + source.alpha()) - alpha() * source.alpha();
byte r = (red() * alpha() * (255 - source.alpha()) + 255 * source.alpha() * source.red()) / d;
byte g = (green() * alpha() * (255 - source.alpha()) + 255 * source.alpha() * source.green()) / d;
byte b = (blue() * alpha() * (255 - source.alpha()) + 255 * source.alpha() * source.blue()) / d;
byte a = d / 255;
return Color(r, g, b, a);
}
RGBA32 value() const { return m_value; }
private:
explicit Color(RGBA32 rgba) : m_value(rgba) { }
RGBA32 m_value { 0 };
};