Lesson 04 · The 64x32 framebuffer - Build a CHIP-8 Emulator

The 64x32 framebuffer

CHIP-8's screen is a tiny 64x32 grid of pixels that are either on or off. Today you build that framebuffer with pixel set, get, and clear, the surface every draw instruction will paint onto.

The goal

Build a 64x32 monochrome framebuffer with set-pixel, get-pixel, and clear.

Start here - the target

TO DO

Scenario: Pixels turn on, read back, and clear

Givena new VM with a blank display

Whenthe pixel at column 10, row 5 is set on

Thenreading that pixel returns on (true) and the pixel at column 0, row 0 reads off (false)

Andafter ClearDisplay every one of the 64x32 pixels reads off

Background

CHIP-8 draws to a monochrome display just 64 pixels wide and 32 pixels tall. Each pixel is a single bit: on or off, nothing in between. That makes the framebuffer a flat grid of 64 * 32 = 2048 cells, and every graphics instruction the machine has ultimately reduces to flipping cells in this grid.

Store it however you like as long as (x, y) maps to one cell - a row-major array indexed by y*64 + x is the simplest. The three operations you build today are the whole display API: turn a pixel on or off, ask whether one is on, and blank the entire screen. The 00E0 opcode will call clear, and the DXYN draw opcode will call set thousands of times, but neither needs anything more than this.

Make it work

const (W, H = 64, 32)
type VM struct {
  // ... mem, V ...
  display [W * H]bool // row-major: index = y*W + x
}
func (v *VM) SetPixel(x, y int, on bool) { v.display[y*W+x] = on }
func (v *VM) GetPixel(x, y int) bool { return v.display[y*W+x] }
func (v *VM) ClearDisplay() { v.display = [W * H]bool{} }

CheckpointDONE

The VM has a 64x32 framebuffer you can set, read, and clear. Commit and stop here.