Fold the leftover formatters into the SI ones and stop reallocating the draw scratch

fb.go

@@ -32,13 +32,14 @@ type scanout struct {
 // w and h are the logical canvas, which is portrait; pw and ph are the panel,
 // which is landscape.
 type framebuffer struct {
-	fd     int
-	back   []byte
-	w      int
-	h      int
-	pw     int
-	ph     int
-	stride int
+	fd      int
+	back    []byte
+	scratch []byte
+	w       int
+	h       int
+	pw      int
+	ph      int
+	stride  int
 
 	bufs   [scanoutBuffers]scanout
 	front  int
@@ -252,6 +253,7 @@ func openFramebuffer() (*framebuffer, error) {
 		}
 	}
 	fb.back = make([]byte, fb.stride*fb.ph)
+	fb.scratch = make([]byte, fb.stride)
 
 	set := drm.ModeCrtc{
 		SetConnectorsPtr: uint64(uintptr(unsafe.Pointer(&fb.connID))),
@@ -316,15 +318,22 @@ type rgb struct {
 
 func pixel(c rgb) uint32 { return drm.Pack(c.r, c.g, c.b) }
 
-func (fb *framebuffer) fill(c rgb) {
+// A run of one repeated pixel, reused between calls: a whole panel row is the
+// longest anything here needs, and every draw is on the one render goroutine.
+func (fb *framebuffer) pixelRun(n int, c rgb) []byte {
 	v := pixel(c)
-	row := make([]byte, fb.stride)
-	for x := 0; x+4 <= fb.stride; x += 4 {
-		row[x+0] = byte(v)
-		row[x+1] = byte(v >> 8)
-		row[x+2] = byte(v >> 16)
-		row[x+3] = byte(v >> 24)
+	s := fb.scratch[:n]
+	for i := 0; i+4 <= n; i += 4 {
+		s[i+0] = byte(v)
+		s[i+1] = byte(v >> 8)
+		s[i+2] = byte(v >> 16)
+		s[i+3] = byte(v >> 24)
 	}
+	return s
+}
+
+func (fb *framebuffer) fill(c rgb) {
+	row := fb.pixelRun(fb.stride, c)
 	for y := 0; y < fb.ph; y++ {
 		copy(fb.back[y*fb.stride:], row)
 	}
@@ -337,14 +346,7 @@ func (fb *framebuffer) rect(x0, y0, w, h int, c rgb) {
 	if x0 >= x1 || y0 >= y1 {
 		return
 	}
-	v := pixel(c)
-	span := make([]byte, (y1-y0)*4)
-	for i := 0; i+4 <= len(span); i += 4 {
-		span[i+0] = byte(v)
-		span[i+1] = byte(v >> 8)
-		span[i+2] = byte(v >> 16)
-		span[i+3] = byte(v >> 24)
-	}
+	span := fb.pixelRun((y1-y0)*4, c)
 	for x := x0; x < x1; x++ {
 		copy(fb.back[fb.offset(x, y1-1):], span)
 	}