Pass through pen get for PicoVision

Now there's at least some way to read from the screen surface

32blit-pico/display_picovision.cpp

@@ -213,6 +213,16 @@ static void blit_rgba_rgb555_picovision(const blit::Surface* src, uint32_t soff,
   } while(cnt);
 }
 
+template<int h_repeat = 1>
+static blit::Pen get_pen_rgb555_picovision(const blit::Surface *surf, uint32_t offset) {
+  uint32_t tmp;
+  ram.read_blocking(base_address + offset * h_repeat * 2, &tmp, 1);
+
+  uint8_t r, g, b;
+  unpack_rgb555(tmp, r, g, b);
+  return {r, g, b};
+}
+
 static void write_frame_setup(uint16_t width, uint16_t height, blit::PixelFormat format, uint8_t h_repeat, uint8_t v_repeat) {
   constexpr int buf_size = 32;
   uint32_t buf[buf_size];
@@ -347,9 +357,11 @@ void display_mode_changed(blit::ScreenMode new_mode, blit::SurfaceTemplate &new_
   if(new_surf_template.bounds.w <= 160) {
     new_surf_template.pen_blend = pen_rgba_rgb555_picovision<2>;
     new_surf_template.blit_blend = blit_rgba_rgb555_picovision<2>;
+    new_surf_template.pen_get = get_pen_rgb555_picovision<2>;
   } else {
     new_surf_template.pen_blend = pen_rgba_rgb555_picovision;
     new_surf_template.blit_blend = blit_rgba_rgb555_picovision;
+    new_surf_template.pen_get = get_pen_rgb555_picovision;
   }
 
   need_mode_change = 2; // make sure to update both banks

32blit/engine/api_private.hpp

@@ -28,6 +28,7 @@ namespace blit {
 
     PenBlendFunc pen_blend = nullptr;
     BlitBlendFunc blit_blend = nullptr;
+    PenGetFunc pen_get = nullptr;
   };
 
   // subset of Surface for API compat

32blit/engine/engine.cpp

@@ -36,6 +36,9 @@ namespace blit {
     if(new_screen.blit_blend)
       screen.bbf = new_screen.blit_blend;
 
+    if(new_screen.pen_get)
+      screen.pgf = new_screen.pen_get;
+
     return true;
   }