feat: primitive styling

client/world/drawer.go

@@ -67,18 +67,13 @@ type PrimitiveDrawer interface {
 	// Fill renders the current path using the current fill state.
 	Fill()
 
-	// CopyShift shifts the current backing image by (dx, dy) in canvas pixels.
-	// dx > 0 shifts the image to the right, dy > 0 shifts the image down.
-	// Newly exposed areas are cleared to transparent.
+	// CopyShift shifts backing pixels by (dx,dy). Newly exposed areas become transparent/undefined;
+	// caller is expected to ClearRectTo() the dirty areas before drawing.
 	CopyShift(dx, dy int)
 
-	// ClearAll clears the entire backing canvas to transparent.
-	// Must NOT affect the current clip state.
-	ClearAll()
-
-	// ClearRect clears a pixel rectangle to transparent.
-	// Must NOT affect the current clip state.
-	ClearRect(x, y, w, h int)
+	// Clear operations must NOT change clip state.
+	ClearAllTo(bg color.Color)
+	ClearRectTo(x, y, w, h int, bg color.Color)
 }
 
 // ggClipRect stores one clip rectangle in canvas pixel coordinates.
@@ -283,44 +278,61 @@ func (d *GGDrawer) CopyShift(dx, dy int) {
 	copy(img.Pix, d.scratch.Pix)
 }
 
-// ClearAll clears the whole RGBA backing image to transparent.
-// It does not touch gg clip state.
-func (d *GGDrawer) ClearAll() {
+func (d *GGDrawer) ClearAllTo(bg color.Color) {
 	img, ok := d.DC.Image().(*image.RGBA)
 	if !ok || img == nil {
-		panic("GGDrawer.ClearAll: backing image is not *image.RGBA")
+		panic("GGDrawer.ClearAllTo: backing image is not *image.RGBA")
 	}
-	for i := range img.Pix {
-		img.Pix[i] = 0
+
+	r, g, b, a := bg.RGBA()
+	// Convert from 16-bit range to 8-bit.
+	R := byte(r >> 8)
+	G := byte(g >> 8)
+	B := byte(b >> 8)
+	A := byte(a >> 8)
+
+	p := img.Pix
+	for i := 0; i+3 < len(p); i += 4 {
+		p[i+0] = R
+		p[i+1] = G
+		p[i+2] = B
+		p[i+3] = A
 	}
 }
 
-// ClearRect clears a region to transparent. It does not touch gg clip state.
-// Rectangle is clamped to the image bounds.
-func (d *GGDrawer) ClearRect(x, y, w, h int) {
+func (d *GGDrawer) ClearRectTo(x, y, w, h int, bg color.Color) {
 	if w <= 0 || h <= 0 {
 		return
 	}
+
 	img, ok := d.DC.Image().(*image.RGBA)
 	if !ok || img == nil {
-		panic("GGDrawer.ClearRect: backing image is not *image.RGBA")
+		panic("GGDrawer.ClearRectTo: backing image is not *image.RGBA")
 	}
 
-	b := img.Bounds()
-	x0 := max(x, b.Min.X)
-	y0 := max(y, b.Min.Y)
-	x1 := min(x+w, b.Max.X)
-	y1 := min(y+h, b.Max.Y)
+	bounds := img.Bounds()
+	x0 := max(x, bounds.Min.X)
+	y0 := max(y, bounds.Min.Y)
+	x1 := min(x+w, bounds.Max.X)
+	y1 := min(y+h, bounds.Max.Y)
 	if x0 >= x1 || y0 >= y1 {
 		return
 	}
 
-	// Zero rows.
+	r, g, b, a := bg.RGBA()
+	R := byte(r >> 8)
+	G := byte(g >> 8)
+	B := byte(b >> 8)
+	A := byte(a >> 8)
+
+	rowBytes := (x1 - x0) * 4
 	for yy := y0; yy < y1; yy++ {
 		off := yy*img.Stride + x0*4
-		n := (x1 - x0) * 4
-		for i := 0; i < n; i++ {
-			img.Pix[off+i] = 0
+		for i := 0; i < rowBytes; i += 4 {
+			img.Pix[off+i+0] = R
+			img.Pix[off+i+1] = G
+			img.Pix[off+i+2] = B
+			img.Pix[off+i+3] = A
 		}
 	}
 }