change(png): Change from 565+alpha to RGB5551

pycardium/modules/py/png.py

 import sys_png
 import color
 
+RGB8 = 0
+RGBA8 = 1
+RGB565 = 2
+RGBA5551 = 3
+
 
 def decode(png_data, format="RGB", bg=color.BLACK):
     """
@@ -8,17 +13,17 @@ def decode(png_data, format="RGB", bg=color.BLACK):
 
     :param str format: The intended output format:
 
-       - ``RGB``: 24 bit RGB.
-       - ``RGBA``: 24 bit RGB + 8 bit alpha.
-       - ``565``: 16 bit RGB. This consumes 1 byte less RAM per pixel than ``RGB``.
-       - ``565A``: 16 bit RGB + 8 bit alpha.
+       - ``png.RGB8``: 24 bit RGB.
+       - ``png.RGBA8``: 24 bit RGB + 8 bit alpha.
+       - ``png.RGB565``: 16 bit RGB. This consumes 1 byte less RAM per pixel than ``png.RGB8``.
+       - ``png.RGBA5551``: 15 bit RGB + 1 bit alpha.
 
-       Default is ``RGB``.
+       Default is ``png.RGB8``.
 
     :param Color bg: Background color.
 
       If the PNG contains an alpha channel but no alpha
-      channel is requested in the output (``RGB`` or ``565``)
+      channel is requested in the output (``png.RGB8`` or ``png.RGB565``)
       this color will be used as the background color.
 
       Default is ``Color.BLACK``.
@@ -27,7 +32,7 @@ def decode(png_data, format="RGB", bg=color.BLACK):
 
     .. versionadded:: 1.17
 
-    **Example with RGB data:**
+    **Example with RGBA8 data:**
 
     .. code-block:: python
 
@@ -36,15 +41,15 @@ def decode(png_data, format="RGB", bg=color.BLACK):
 
        # Draw a PNG file to the display
        f = open("example.png")
-       w, h, img = png.decode(f.read())
+       w, h, img = png.decode(f.read(), png.RGBA8)
        f.close()
        with display.open() as d:
            d.clear()
-           d.blit(0, 0, w, h, img)
+           d.blit(0, 0, w, h, img, display.RGBA8)
            d.update()
 
 
-    **Example with rgb565 data:**
+    **Example with RGB565 data:**
 
     .. code-block:: python
 
@@ -53,24 +58,24 @@ def decode(png_data, format="RGB", bg=color.BLACK):
 
        # Draw a PNG file to the display
        f = open("example.png")
-       w, h, img = png.decode(f.read(), "565")
+       w, h, img = png.decode(f.read(), png.RGB565)
        f.close()
        with display.open() as d:
            d.clear()
-           d.blit(0, 0, w, h, img, True)
+           d.blit(0, 0, w, h, img, True, display.RGB565)
            d.update()
 
     """
 
-    formats = ("RGB", "RGBA", "565", "565A")
+    formats = (RGB8, RGBA8, RGB565, RGBA5551)
     if format not in formats:
-        raise ValueError("Supported formats: " + ",".join(formats))
+        raise ValueError("Output format not supported")
 
-    if format == "RGB":
-        return sys_png.decode(png_data, 0, 0, bg)
-    if format == "RGBA":
-        return sys_png.decode(png_data, 0, 1, bg)
-    if format == "565":
+    if format == RGB8:
         return sys_png.decode(png_data, 1, 0, bg)
-    if format == "565A":
+    if format == RGBA8:
         return sys_png.decode(png_data, 1, 1, bg)
+    if format == RGB565:
+        return sys_png.decode(png_data, 0, 0, bg)
+    if format == RGBA5551:
+        return sys_png.decode(png_data, 0, 1, bg)

pycardium/modules/sys_png.c

@@ -36,7 +36,18 @@ static void lode_raise(unsigned int status)
 	}
 }
 
-static inline uint16_t rgb888_to_rgb565(uint8_t *bytes)
+static inline uint16_t rgba8_to_rgba5551(uint8_t *bytes)
+{
+	uint16_t c = ((bytes[0] & 0b11111000) << 8) |
+		     ((bytes[1] & 0b11111000) << 3) |
+		     ((bytes[2] & 0b11111000) >> 2);
+	if (bytes[3] > 127) {
+		c |= 1;
+	}
+	return c;
+}
+
+static inline uint16_t rgb8_to_rgb565(uint8_t *bytes)
 {
 	return ((bytes[0] & 0b11111000) << 8) | ((bytes[1] & 0b11111100) << 3) |
 	       (bytes[2] >> 3);
@@ -64,7 +75,7 @@ static mp_obj_t mp_png_decode(size_t n_args, const mp_obj_t *args)
 	mp_buffer_info_t png_info;
 
 	mp_obj_t png       = args[0];
-	mp_obj_t rgb565_out = args[1];
+	mp_obj_t rgb8_out  = args[1];
 	mp_obj_t alpha_out = args[2];
 	mp_obj_t bg        = args[3];
 
@@ -128,23 +139,22 @@ static mp_obj_t mp_png_decode(size_t n_args, const mp_obj_t *args)
 		raw_len = w * h * 3;
 	}
 
-	if (mp_obj_is_true(rgb565_out)) {
+	if (!mp_obj_is_true(rgb8_out)) {
 		if (mp_obj_is_true(alpha_out)) {
-			for (i = 0, j = 0; i < raw_len; i += 4, j += 3) {
-				uint16_t c = rgb888_to_rgb565(&raw[i]);
+			for (i = 0, j = 0; i < raw_len; i += 4, j += 2) {
+				uint16_t c = rgba8_to_rgba5551(&raw[i]);
 				raw[j]     = c & 0xFF;
 				raw[j + 1] = c >> 8;
 				raw[j + 2] = raw[i + 3];
 			}
-			raw_len = w * h * 3;
 		} else {
 			for (i = 0, j = 0; i < raw_len; i += 3, j += 2) {
-				uint16_t c = rgb888_to_rgb565(&raw[i]);
+				uint16_t c = rgb8_to_rgb565(&raw[i]);
 				raw[j]     = c & 0xFF;
 				raw[j + 1] = c >> 8;
 			}
-			raw_len = w * h * 2;
 		}
+		raw_len = w * h * 2;
 	}
 
 	if (raw_len != raw_len_original) {