feat(demo): exercise affine transforms and raster distortion

src/affine_raster_demo.rs

@@ -0,0 +1,40 @@
+//! CPU-driven affine raster distortion. HBlank DMA changes BG2PB for the next
+//! line transition; internal origins accumulate the resulting horizontal shifts.
+
+use crate::{
+    graphics_demo::{GraphicsDemo, GraphicsError},
+    input::Buttons,
+    machine::Machine,
+    memory::MemoryError,
+    video::Framebuffer,
+};
+
+/// Completed updates and signed pan X/Y, as three debug words.
+pub const AFFINE_RASTER_STATE: u32 = crate::affine_demo::AFFINE_STATE;
+/// 160 halfwords generated by ARM code during each VBlank.
+pub const AFFINE_RASTER_TABLE: u32 = 0x0200_1000;
+
+pub struct AffineRasterDemo {
+    runner: GraphicsDemo,
+}
+
+impl AffineRasterDemo {
+    pub fn new() -> Result<Self, MemoryError> {
+        Ok(Self {
+            runner: GraphicsDemo::with_program(crate::affine_demo::raster_program())?,
+        })
+    }
+
+    pub fn machine(&self) -> &Machine {
+        self.runner.machine()
+    }
+
+    /// Arrows pan; Q rotates; W zooms; Z bypasses raster distortion; Enter resets pan.
+    pub fn frame(
+        &mut self,
+        buttons: Buttons,
+        output: &mut Framebuffer,
+    ) -> Result<usize, GraphicsError> {
+        self.runner.frame_with_control(buttons, output, 0x402)
+    }
+}