movement and sprite flipping

Add sprite clip animation player + unit tests

engine/input.odin

@@ -0,0 +1,28 @@
+package engine
+
+import sdl "vendor:sdl3"
+
+Key :: enum {
+	A,
+	D,
+	Left,
+	Right,
+}
+
+key_down :: proc(key: Key) -> bool {
+	keys := sdl.GetKeyboardState(nil)
+	if keys == nil do return false
+
+	scan_code: sdl.Scancode
+	switch key {
+	case .A:
+		scan_code = .A
+	case .D:
+		scan_code = .D
+	case .Left:
+		scan_code = .LEFT
+	case .Right:
+		scan_code = .RIGHT
+	}
+	return keys[scan_code]
+}

engine/sprite.odin

@@ -11,6 +11,7 @@ Sprite :: struct {
 	clip:     string,
 	frame:    int,
 	time:     f32,
+	flip_x:   bool,
 }
 
 spawn_sprite :: proc(
@@ -99,9 +100,10 @@ draw_sprite :: proc(app: ^App, sprite: ^Sprite) {
 	fw := f32(rect[2])
 	fh := f32(rect[3])
 
-	// Feet-centered placement, same as renderer version
+	pivot := sprite.data.def.pivot
-	x0_px := sprite.position.x - fw * 0.5
+	origin := sprite_quad_origin(sprite.position, {fw, fh}, pivot)
-	y0_px := sprite.position.y - fh
+	x0_px := origin.x
+	y0_px := origin.y
 	x1_px := x0_px + fw
 	y1_px := y0_px + fh
 
@@ -118,6 +120,7 @@ draw_sprite :: proc(app: ^App, sprite: ^Sprite) {
 	v0 := f32(rect[1]) / tex_h
 	u1 := f32(rect[0] + rect[2]) / tex_w
 	v1 := f32(rect[1] + rect[3]) / tex_h
+	if sprite.flip_x do u0, u1 = u1, u0
 
 	// Two triangles: (0,1,2) and (0,2,3)
 	verts := [6]Vertex {
@@ -191,3 +194,12 @@ set_sprite_clip :: proc(sprite: ^Sprite, clip: string) {
 	sprite.frame = 0
 	sprite.time = 0
 }
+
+sprite_quad_origin :: proc(position: Vec2, size: Vec2, pivot: [2]f32) -> Vec2 {
+	return {position.x - size.x * pivot[0], position.y - size.y * pivot[1]}
+}
+
+set_sprite_flip_x :: proc(sprite: ^Sprite, flip: bool) {
+	if sprite == nil do return
+	sprite.flip_x = flip
+}

engine/sprite_test.odin

@@ -19,3 +19,17 @@ to_clip_corners :: proc(t: ^testing.T) {
 	testing.expect_value(t, p[0], f32(0))
 	testing.expect_value(t, p[1], f32(0))
 }
+
+@(test)
+sprite_quad_origin_feet :: proc(t: ^testing.T) {
+	o := sprite_quad_origin({400, 500}, {100, 200}, {0.5, 1.0})
+	testing.expect_value(t, o.x, f32(350))
+	testing.expect_value(t, o.y, f32(300))
+}
+
+@(test)
+sprite_quad_origin_center :: proc(t: ^testing.T) {
+	o := sprite_quad_origin({400, 500}, {100, 200}, {0.5, 0.5})
+	testing.expect_value(t, o.x, f32(350))
+	testing.expect_value(t, o.y, f32(400))
+}

examples/toad/main.odin

@@ -15,12 +15,30 @@ main :: proc() {
 	toad := eng.spawn_sprite(&data, {400, 500}, "idle", 0)
 
 	last := eng.now_seconds()
+	SPEED :: f32(200)
 
 	for eng.events() {
 		now := eng.now_seconds()
 		dt := f32(now - last)
 		last = now
 
+		left := eng.key_down(.A) || eng.key_down(.Left)
+		right := eng.key_down(.D) || eng.key_down(.Right)
+
+		if left || right {
+			eng.set_sprite_clip(&toad, "walk")
+			if left {
+				toad.position.x -= SPEED * dt
+				toad.flip_x = true
+			}
+
+			if right {
+				toad.position.x += SPEED * dt
+				toad.flip_x = false
+			}
+		} else {
+			eng.set_sprite_clip(&toad, "idle")
+		}
 		eng.update_sprite(&toad, dt)
 
 		eng.begin_frame(&app)