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Implement proper alpha-blending of SVG icons (#7011)

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* Implement proper alpha-blending of SVG icons

Also, instead of doing that every time, cache a pre-composited version
that matches the screen's BB type.
This is faster, and also has the advantage of making icon highlights
behave.

Jot down a few notes about corner-cases or future improvements, e.g.,
dimming icons on non-white backgrounds, and nightmode with color icons.
This commit is contained in:
NiLuJe
2020-12-19 22:34:16 +01:00
committed by GitHub
parent a5b133dadc
commit f4e2878a3c
2 changed files with 69 additions and 10 deletions
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2
frontend/ui/widget/iconwidget.lua
View File

@@ -35,7 +35,7 @@ local IconWidget = ImageWidget:extend{
-- be overriden by callers.
width = Screen:scaleBySize(DGENERIC_ICON_SIZE), -- our icons are square
height = Screen:scaleBySize(DGENERIC_ICON_SIZE),
alpha = true, -- our icons have a transparent background
alpha = false, --- @note: our icons have a transparent background, but we flatten them at caching time, and this flag is only checked at blitting time.
is_icon = true, -- avoid dithering in ImageWidget:paintTo()
}

77
frontend/ui/widget/imagewidget.lua
View File

@@ -178,6 +178,45 @@ function ImageWidget:_loadfile()
self._bb = RenderImage:scaleBlitBuffer(self._bb, math.floor(bb_w * DPI_SCALE), math.floor(bb_h * DPI_SCALE))
end
end
-- Now, if that was *also* one of our icons, and it has an alpha channel,
-- compose it against a background-colored BB now, and cache *that*.
-- This helps us avoid repeating alpha-blending steps down the line,
-- and also ensures icon highlights/unhilights behave sensibly.
if self.is_icon then
local bbtype = self._bb:getType()
if bbtype == Blitbuffer.TYPE_BB8A or bbtype == Blitbuffer.TYPE_BBRGB32 then
local icon_bb = Blitbuffer.new(self._bb.w, self._bb.h, Screen.bb:getType())
--- @note: Should match the background color. Which is currently hard-coded as white ;).
--- See the note below in paintTo for how to make the dim flag behave in case
--- this no longer actually is white ;).
icon_bb:fill(Blitbuffer.COLOR_WHITE)
-- And now simply compose the icon on top of that, with dithering if necessary
-- Remembering that NanoSVG feeds us straight alpha, unlike MµPDF
if self._is_straight_alpha then
if Screen.sw_dithering then
icon_bb:ditheralphablitFrom(self._bb, 0, 0, 0, 0, icon_bb.w, icon_bb.h)
else
icon_bb:alphablitFrom(self._bb, 0, 0, 0, 0, icon_bb.w, icon_bb.h)
end
else
if Screen.sw_dithering then
icon_bb:ditherpmulalphablitFrom(self._bb, 0, 0, 0, 0, icon_bb.w, icon_bb.h)
else
icon_bb:pmulalphablitFrom(self._bb, 0, 0, 0, 0, icon_bb.w, icon_bb.h)
end
end
-- Free the original icon w/ an alpha-channel, keep the flattened one
self._bb:free()
self._bb = icon_bb
-- There's no longer an alpha channel ;)
self._is_straight_alpha = nil
end
end
if not self.file_do_cache then
self._bb_disposable = true -- we made it, we can modify and free it
else
@@ -384,20 +423,26 @@ function ImageWidget:paintTo(bb, x, y)
end
end
if do_alpha then
-- NOTE: MuPDF feeds us premultiplied alpha (and we don't care w/ GifLib, as alpha is all or nothing),
-- but NanoSVG feeds us straight alpha
--- @note: MuPDF feeds us premultiplied alpha (and we don't care w/ GifLib, as alpha is all or nothing),
--- while NanoSVG feeds us straight alpha.
--- SVG icons are currently flattened at caching time, so we'll only go through the straight alpha
--- codepath for non-icons SVGs.
if self._is_straight_alpha then
--- @todo if Screen.sw_dithering then use bb:ditheralphablitFrom() when it's available
bb:alphablitFrom(self._bb, x, y, self._offset_x, self._offset_y, size.w, size.h)
--- @note: Our icons are already dithered properly, either at encoding time, or at caching time.
if Screen.sw_dithering and not self.is_icon then
bb:ditheralphablitFrom(self._bb, x, y, self._offset_x, self._offset_y, size.w, size.h)
else
bb:alphablitFrom(self._bb, x, y, self._offset_x, self._offset_y, size.w, size.h)
end
else
if Screen.sw_dithering then
if Screen.sw_dithering and not self.is_icon then
bb:ditherpmulalphablitFrom(self._bb, x, y, self._offset_x, self._offset_y, size.w, size.h)
else
bb:pmulalphablitFrom(self._bb, x, y, self._offset_x, self._offset_y, size.w, size.h)
end
end
else
if Screen.sw_dithering then
if Screen.sw_dithering and not self.is_icon then
bb:ditherblitFrom(self._bb, x, y, self._offset_x, self._offset_y, size.w, size.h)
else
bb:blitFrom(self._bb, x, y, self._offset_x, self._offset_y, size.w, size.h)
@@ -406,13 +451,27 @@ function ImageWidget:paintTo(bb, x, y)
if self.invert then
bb:invertRect(x, y, size.w, size.h)
end
--- @note: This is mainly geared at black icons/text on a *white* background,
--- otherwise the background color itself will shift.
--- i.e., this actually *lightens* the rectangle, but since it's aimed at black,
--- it makes it gray, dimmer; hence the name.
--- TL;DR: If we one day want that to work for icons on a non-white background,
--- a better solution would probably be to take the icon pixmap as an alpha-mask,
--- (which simply involves blending it onto a white background, then inverting the result),
--- and colorBlit it a dim gray onto the target bb.
--- This would require the *original* transparent icon, not the flattened one in the cache.
--- c.f., https://github.com/koreader/koreader/pull/6937#issuecomment-748372429 for a PoC
if self.dim then
bb:dimRect(x, y, size.w, size.h)
end
-- If in night mode, invert all rendered images, so the original is
-- In night mode, invert all rendered images, so the original is
-- displayed when the whole screen is inverted by night mode.
-- Except for our black & white icon files, that we do want inverted
-- in night mode.
-- Except for our *black & white* icons: we do *NOT* want to invert them again:
-- they should match the UI's text/backgound.
--- @note: As for *color* icons, we really *ought* to invert them here,
--- but we currently don't, as we don't really trickle down
--- a way to discriminate them from the B&W ones.
--- Currently, this is *only* the KOReader icon in Help, AFAIK.
if Screen.night_mode and not self.is_icon then
bb:invertRect(x, y, size.w, size.h)
end