Adding SSD1306 OLED display controller support

controller/ssd1306/buffer.go

@@ -0,0 +1,98 @@
+package ssd1306
+
+import "errors"
+
+// Buffer abstracts "drawing" into an 8-row page space for Display calls into an SSD1306.
+// A suitably-sized instance is created using NewBuffer on an SSD1306 instance.
+type Buffer interface {
+	On(x, y int) error
+	Off(x, y int) error
+	Set(x, y int, on bool) error
+	FillRect(x, y int, w, h int) error
+	ClearRect(x, y int, w, h int) error
+	Cells() []byte
+}
+
+// bufferHoriz is a Buffer that operates in memory mode of SSD1306_MEMORYMODE_HORIZ
+type bufferHoriz struct {
+	cells []byte
+	width uint
+	pages uint
+}
+
+func newBuffer(width, pages uint, memoryMode int) Buffer {
+	switch memoryMode {
+	case SSD1306_MEMORYMODE_HORIZ:
+		return newBufferHoriz(width, pages)
+	}
+
+	return nil
+}
+
+func newBufferHoriz(width, pages uint) *bufferHoriz {
+	return &bufferHoriz{
+		width: width,
+		pages: pages,
+		cells: make([]byte, width*pages),
+	}
+}
+
+func (b *bufferHoriz) Cells() []byte {
+	return b.cells
+}
+
+func (b *bufferHoriz) On(x, y int) error {
+	return b.Set(x, y, true)
+}
+
+func (b *bufferHoriz) Off(x, y int) error {
+	return b.Set(x, y, false)
+}
+
+func (b *bufferHoriz) Set(x, y int, on bool) error {
+	if uint(x) > b.width {
+		return errors.New("x cannot be greater than buffer width")
+	}
+	page := uint(y) >> 3
+	if page > b.pages {
+		return errors.New("y cannot be greater than buffer height")
+	}
+
+	index := uint(page*b.width) + uint(x)
+	cell := b.cells[index]
+
+	bit := byte(1) << (uint(y) & 0x7)
+	if on {
+		cell |= bit
+	} else {
+		cell &^= bit
+	}
+
+	b.cells[index] = cell
+
+	return nil
+}
+
+func (b *bufferHoriz) FillRect(x, y int, w, h int) error {
+	for xi := 0; xi < w; xi++ {
+		for yi := 0; yi < h; yi++ {
+			if err := b.Set(x+xi, y+yi, true); err != nil {
+				return err
+			}
+		}
+	}
+
+	return nil
+}
+
+func (b *bufferHoriz) ClearRect(x, y int, w, h int) error {
+	for xi := 0; xi < w; xi++ {
+		for yi := 0; yi < h; yi++ {
+			if err := b.Set(x+xi, y+yi, false); err != nil {
+				return err
+			}
+		}
+	}
+
+	return nil
+}