Inky 7.3: Add ordered dither support.

Author: Gadgetoid

libraries/pico_graphics/pico_graphics.hpp

@@ -499,6 +499,32 @@ namespace pimoroni {
 
   class PicoGraphics_PenInky7 : public PicoGraphics {
     public:
+      static const uint16_t palette_size = 8;
+      RGB palette[8] = {
+        /*
+        {0x2b, 0x2a, 0x37},
+        {0xdc, 0xcb, 0xba},
+        {0x35, 0x56, 0x33},
+        {0x33, 0x31, 0x47},
+        {0x9c, 0x3b, 0x2e},
+        {0xd3, 0xa9, 0x34},
+        {0xab, 0x58, 0x37},
+        {0xb2, 0x8e, 0x67}
+        */
+        {  0,   0,   0}, // black
+        {255, 255, 255}, // white
+        {  0, 255,   0}, // green
+        {  0,   0, 255}, // blue
+        {255,   0,   0}, // red
+        {255, 255,   0}, // yellow
+        {255, 128,   0}, // orange
+        {220, 180, 200}  // clean / taupe?!
+      };
+
+      std::array<std::array<uint8_t, 16>, 512> candidate_cache;
+      bool cache_built = false;
+      std::array<uint8_t, 16> candidates;
+    
       RGB src_color;
       RGB565 color;
       IDirectDisplayDriver<uint8_t> &driver;
@@ -510,6 +536,10 @@ namespace pimoroni {
       int create_pen(uint8_t r, uint8_t g, uint8_t b) override;
       void set_pixel(const Point &p) override;
       void set_pixel_span(const Point &p, uint l) override;
+
+      void get_dither_candidates(const RGB &col, const RGB *palette, size_t len, std::array<uint8_t, 16> &candidates);
+      void set_pixel_dither(const Point &p, const RGB &c) override;
+
       void frame_convert(PenType type, conversion_callback_func callback) override;
       static size_t buffer_size(uint w, uint h) {
         return w * h;

libraries/pico_graphics/pico_graphics_pen_inky7.cpp

@@ -20,6 +20,49 @@ namespace pimoroni {
   void PicoGraphics_PenInky7::set_pixel_span(const Point &p, uint l) {
     driver.write_pixel_span(p, l, color);
   }
+  void PicoGraphics_PenInky7::get_dither_candidates(const RGB &col, const RGB *palette, size_t len, std::array<uint8_t, 16> &candidates) {
+    RGB error;
+    for(size_t i = 0; i < candidates.size(); i++) {
+        candidates[i] = (col + error).closest(palette, len);
+        error += (col - palette[candidates[i]]);
+    }
+
+    // sort by a rough approximation of luminance, this ensures that neighbouring
+    // pixels in the dither matrix are at extreme opposites of luminence
+    // giving a more balanced output
+    std::sort(candidates.begin(), candidates.end(), [palette](int a, int b) {
+        return palette[a].luminance() > palette[b].luminance();
+    });
+  }
+  void PicoGraphics_PenInky7::set_pixel_dither(const Point &p, const RGB &c) {
+    if(!bounds.contains(p)) return;
+
+    if(!cache_built) {
+        for(uint i = 0; i < 512; i++) {
+            uint r = (i & 0x1c0) >> 1;
+            uint g = (i & 0x38) << 2;
+            uint b = (i & 0x7) << 5;
+            RGB cache_col(
+                r | (r >> 3) | (r >> 6),
+                g | (g >> 3) | (g >> 6),
+                b | (b >> 3) | (b >> 6)
+            );
+            get_dither_candidates(cache_col, palette, palette_size, candidate_cache[i]);
+        }
+        cache_built = true;
+    }
+
+    uint cache_key = ((c.r & 0xE0) << 1) | ((c.g & 0xE0) >> 2) | ((c.b & 0xE0) >> 5);
+    //get_dither_candidates(c, palette, 256, candidates);
+
+    // find the pattern coordinate offset
+    uint pattern_index = (p.x & 0b11) | ((p.y & 0b11) << 2);
+
+    // set the pixel
+    //color = candidates[pattern[pattern_index]];
+    color = candidate_cache[cache_key][dither16_pattern[pattern_index]];
+    set_pixel(p);
+  }
   void PicoGraphics_PenInky7::frame_convert(PenType type, conversion_callback_func callback) {
     if(type == PEN_INKY7) {
       uint byte_count = bounds.w/2;