[OpenJDK Rasterizer] Fwd: Re: Fwd: RFR: Marlin renderer #3

[Laurent Bourgès]

Jim,

>> Few ideas to discuss:
>> 1/ I wonder now if the gridding = ceil (x/y - 0.5) should be done
>> differently: why not apply the offset to - 0.5 to points before curve
>> decimation or adding lines: it may saves a lot of substractions:
>> AddLine (x1,y1,x2,y2) implies 4 substractions whereas lineTo (x2,y2)
>> only needs to adjust the last point.
>> Idem for curve decimation, shifting points may help.
>
>
> I like this idea - you can bake the translation into the transform that
is applied prior to the rasterizer so there is no added work being done.

Will try asap, maybe tonight. I mean I will shift coordinates early in
tosubpixx() and tosubpixy () by -0.5f.

>> - do you know if the breakCurveAndAddLines (quad or cubic) really takes
>> into account the supersampling scale to generate only segments needed
>> and no more ?
>
>
> I don't remember.  I'd have to read the code and figure it out.

Thanks, it seems there are some thresholds BND... but I am unable to find
out what it is related to ?

>> - I use fixed-point (32.32 + error) as you did but it is maybe too
>> precise: the slope, bumpx and error could be determined from integer
>> coordinates for starting / ending points = ceil (x1 - 0.5), ceil (y -
>> 0.5) directly
>
>
> I don't understand what you are getting at here...?

I wonder if Renderer class could use 24.8 fixed point coordinates early in
tosubpixx() and tosubpixy () to have 1/256 precision in lineTo, curveTo,
quadTo before addLine and curve culling to get rid of floating-point maths
early.

int (24.8) = (int) ( float * 256f)

It is less correct than ceil ( float * 256f - 0.5) but surely enough to
maintain 1/8 precision. Of course, it will limit the output image to 2^24 =
16M pixel in both directions but is is large enough.

I will make some experiments in the PathConsumer implemented by Renderer:

private static float tosubpixx(final float pix_x) { return
f_SUBPIXEL_POSITIONS_X * pix_x; }
private static float tosubpixy(final float pix_y) { return
f_SUBPIXEL_POSITIONS_Y * pix_y; }

@Override public void moveTo(float pix_x0, float pix_y0) { closePath();
this.pix_sx0 = pix_x0; this.pix_sy0 = pix_y0; this.y0 = tosubpixy(pix_y0);
this.x0 = tosubpixx(pix_x0); }

@Override public void lineTo(float pix_x1, float pix_y1) { float x1 =
tosubpixx(pix_x1); float y1 = tosubpixy(pix_y1); addLine(x0, y0, x1, y1);
x0 = x1; y0 = y1; }

@Override public void curveTo(float x1, float y1, float x2, float y2, float
x3, float y3) { final float xe = tosubpixx(x3); final float ye =
tosubpixy(y3); curve.set(x0, y0, tosubpixx(x1), tosubpixy(y1),
tosubpixx(x2), tosubpixy(y2), xe, ye); curveBreakIntoLinesAndAdd(x0, y0,
curve, xe, ye); x0 = xe; y0 = ye; }

@Override public void quadTo(float x1, float y1, float x2, float y2) {
final float xe = tosubpixx(x2); final float ye = tosubpixy(y2);
curve.set(x0, y0, tosubpixx(x1), tosubpixy(y1), xe, ye);
quadBreakIntoLinesAndAdd(x0, y0, curve, xe, ye); x0 = xe; y0 = ye; }

@Override public void closePath() { // lineTo expects its input in pixel
coordinates. lineTo(pix_sx0, pix_sy0); }

@Override public void pathDone() { closePath(); }

Cheers,
Laurent
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