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https://git.sr.ht/~eliasnaur/gio
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Elias Naur
eb9bf60b09
We're about to let clip.Path use more of the compute renderer features (lines, cubic béziers). This change prepares the gpu package for reading one of several commands types, not just the quadratic béziers of before. The old Quad type is still the basis for the stroking algorithms, but this change moves it into package gpu which is the only user. Signed-off-by: Elias Naur <mail@eliasnaur.com>
97 lines
2.2 KiB
Go
97 lines
2.2 KiB
Go
package gpu
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import (
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"gioui.org/f32"
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)
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type quadSplitter struct {
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bounds f32.Rectangle
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contour uint32
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d *drawOps
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}
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func encodeQuadTo(data []byte, meta uint32, from, ctrl, to f32.Point) {
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// NW.
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encodeVertex(data, meta, -1, 1, from, ctrl, to)
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// NE.
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encodeVertex(data[vertStride:], meta, 1, 1, from, ctrl, to)
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// SW.
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encodeVertex(data[vertStride*2:], meta, -1, -1, from, ctrl, to)
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// SE.
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encodeVertex(data[vertStride*3:], meta, 1, -1, from, ctrl, to)
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}
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func encodeVertex(data []byte, meta uint32, cornerx, cornery int16, from, ctrl, to f32.Point) {
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var corner float32
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if cornerx == 1 {
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corner += .5
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}
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if cornery == 1 {
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corner += .25
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}
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v := vertex{
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Corner: corner,
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FromX: from.X,
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FromY: from.Y,
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CtrlX: ctrl.X,
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CtrlY: ctrl.Y,
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ToX: to.X,
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ToY: to.Y,
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}
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v.encode(data, meta)
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}
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func (qs *quadSplitter) encodeQuadTo(from, ctrl, to f32.Point) {
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data := qs.d.writeVertCache(vertStride * 4)
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encodeQuadTo(data, qs.contour, from, ctrl, to)
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}
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func (qs *quadSplitter) splitAndEncode(quad quadSegment) {
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cbnd := f32.Rectangle{
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Min: quad.From,
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Max: quad.To,
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}.Canon()
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from, ctrl, to := quad.From, quad.Ctrl, quad.To
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// If the curve contain areas where a vertical line
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// intersects it twice, split the curve in two x monotone
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// lower and upper curves. The stencil fragment program
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// expects only one intersection per curve.
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// Find the t where the derivative in x is 0.
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v0 := ctrl.Sub(from)
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v1 := to.Sub(ctrl)
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d := v0.X - v1.X
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// t = v0 / d. Split if t is in ]0;1[.
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if v0.X > 0 && d > v0.X || v0.X < 0 && d < v0.X {
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t := v0.X / d
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ctrl0 := from.Mul(1 - t).Add(ctrl.Mul(t))
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ctrl1 := ctrl.Mul(1 - t).Add(to.Mul(t))
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mid := ctrl0.Mul(1 - t).Add(ctrl1.Mul(t))
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qs.encodeQuadTo(from, ctrl0, mid)
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qs.encodeQuadTo(mid, ctrl1, to)
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if mid.X > cbnd.Max.X {
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cbnd.Max.X = mid.X
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}
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if mid.X < cbnd.Min.X {
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cbnd.Min.X = mid.X
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}
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} else {
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qs.encodeQuadTo(from, ctrl, to)
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}
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// Find the y extremum, if any.
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d = v0.Y - v1.Y
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if v0.Y > 0 && d > v0.Y || v0.Y < 0 && d < v0.Y {
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t := v0.Y / d
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y := (1-t)*(1-t)*from.Y + 2*(1-t)*t*ctrl.Y + t*t*to.Y
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if y > cbnd.Max.Y {
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cbnd.Max.Y = y
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}
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if y < cbnd.Min.Y {
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cbnd.Min.Y = y
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}
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}
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qs.bounds = qs.bounds.Union(cbnd)
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}
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