On Mon, 15 Mar 2021 10:25:50 GMT, Dmitry Batrak <dbat...@openjdk.org> wrote:
> This is the implementation used by JetBrains Runtime for the last 4 years,
> after some cleanup, and with one problem,
> found while preparing the pull request, fixed.
> Even though typical scenarios for a UI application should be covered, it's
> not a complete solution. In particular, emoji-s
> still won't be rendered for large font sizes (more than 100pt), and for
> non-trivial composite/painting modes.
> Notable implementation details are listed below.
>
> **Glyph image generation**
>
> Deprecated CGContextShowGlyphsAtPoint function, used by JDK on macOS to
> render text, cannot render emojis,
> CTFontDrawGlyphs is used instead. It ignores the scale component of text
> transformation matrix, so a 'real-sized'
> CTFont object should be passed to it. The same sizing procedure is done when
> calculating glyph metrics, because they
> are not scaled proportionally with font size (as they do for vector fonts).
>
> **Glyph image storage**
>
> Existing GlyphInfo structure is used to store color glyph image. Color glyph
> can be distinguished by having 4 bytes
> of storage per pixel. Color components are stored in pre-multiplied alpha
> format.
>
> **Glyph rendering**
>
> Previously, GlyphList instance always contained glyphs in the same format
> (solid, grayscale or LCD), determined by the
> effective rendering hint. Now the renderers must be prepared to GlyphList
> having 'normal' glyphs interspersed with
> color glyphs (they can appear due to font fallback). This isn't a problem for
> OpenGL renderer (used for on-screen painting),
> but GlyphListLoopPipe-based renderers (used for off-screen painting) needed
> an adjustment to be able to operate on
> specific segments of GlyphList.
> As an incidental optimization, calculation of GlyphList bounds ('getBounds'
> method) is performed now only when needed
> (most text renderers don't need this information).
> Speaking of the actual rendering of the glyph image, it's done by the
> straightforward glDrawPixels call in OpenGL renderer,
> and by re-using existing Blit primitive in off-screen renderers.
>
> **Testing**
>
> There's no good way to test the new functionality automatically, but I've
> added a test verifying that 'something' is
> rendered for the emoji character, when painting to BufferedImage.
>
> Existing tests pass after the change.
src/java.desktop/share/classes/sun/java2d/loops/DrawGlyphListColor.java line 71:
> 69: static {
> 70: GraphicsPrimitiveMgr.registerGeneral(
> 71: new DrawGlyphListColor(null, null, null));
If it is a complete "General" loop which supports all possible combination of
incoming src/comp/dst/transform/etc I suggest to confirm that in the test.
-------------
PR: https://git.openjdk.java.net/jdk/pull/3007
