PNG saves go through pngio; remove pygraphics' own encoder

docs/graphics-files.md

@@ -12,7 +12,7 @@ Built into `pygraphics` — see the [graphics guide](graphics-guide.md):
 | `pygraphics.pbm_to_framebuffer(path)` | PBM (1-bit) |
 | `pygraphics.pgm_to_framebuffer(path)` | PGM (grayscale) |
 | `pygraphics.load_image(path)` | Auto-detect PBM/PGM/BMP from header |
-| `pygraphics.save_image(fb, path)` | Write PBM/PGM/BMP for supported formats |
+| `pygraphics.save_image(fb, path)` | Write PBM/PGM/BMP for supported formats, or PNG for a `.png` name |
 | `pygraphics.FrameBuffer.from_file(path)` | Same as `load_image` |
 | `pygraphics.FrameBuffer.save(path)` | Same as `save_image` |
 | `pygraphics.FrameBuffer.export(path)` / `export_framebuffer` | **Pure-Python only.** Write importable `.py` module (`BITMAP = bytearray(...)`) |
@@ -38,6 +38,8 @@ build, import them from the pure package (`lib/pygraphics/`) instead — see
 | `GS4_HMSB` | PGM (P5, max 15) | 4-bit grayscale |
 | `GS8` | PGM (P5, max 255) | 8-bit grayscale |
 | `RGB565` | BMP | 16-bit RGB565 Windows BMP |
+| `RGB888` | PNG | Always PNG |
+| `RGB565`, `GS8`, `MONO_HLSB` | PNG | When the name ends in `.png` |
 
 `MONO_VLSB`, `MONO_HMSB`, and other display-native formats are not saved directly — convert or blit to a supported buffer first.
 
@@ -71,4 +73,9 @@ From @russhughes st7789py_mpy:
 
 ## PNG
 
-Experimental support in utils — probe with [`tools/png_test.py`](https://github.com/PyDevices/pdwidgets/blob/main/tools/png_test.py) in the pdwidgets repo (CPython only; requires sibling pydevices-examples, `pypng`, and a local checkout of [material-design-icons](https://github.com/google/material-design-icons) with its `png/` tree, or `PDWIDGETS_PNG_DIR`).
+`save_image(fb, "shot.png")` writes PNG through
+[pngio](https://github.com/PyDevices/micropython-pydevices/tree/main/modules/pngio),
+not an encoder of pygraphics' own. PyDevices MicroPython firmware has pngio
+built in. On CPython it comes with `pydevices-desktop` and needs Pillow
+(`pip install pillow`). Without it, saving a PNG raises an `ImportError` that
+says what to install. Every other format works without it.

lib/pygraphics/__init__.py

@@ -68,8 +68,6 @@
     "pbm_to_framebuffer": ("_files", "pbm_to_framebuffer"),
     "pgm_to_framebuffer": ("_files", "pgm_to_framebuffer"),
     "save_image": ("_files", "save_image"),
-    "encode_png": ("_png", "encode_png"),
-    "write_png_file": ("_png", "write_png_file"),
 }
 
 
@@ -128,7 +126,6 @@ def implementation():
     "rect",
     "round_rect",
     "save_image",
-    "encode_png",
     "text",
     "text8",
     "text14",

lib/pygraphics/_files.py

@@ -10,7 +10,6 @@
     RGB888,
     FrameBuffer,
 )
-from ._png import encode_png, write_png_file
 
 # Framebuffer formats that ``save_image`` can write, keyed by file extension.
 _SAVE_FORMATS = {
@@ -73,6 +72,38 @@ def load_image(filename):
     raise ValueError(f"Unsupported image file {filename!r} (header {header!r})")
 
 
+def _save_png(fb, filename):
+    """PNG through pngio: MicroPython's built-in module, or on CPython
+    pydevices-desktop's, over Pillow. pygraphics has no PNG encoder of its own."""
+    try:
+        import pngio
+    except ImportError:
+        raise ImportError(
+            "saving PNG needs pngio: PyDevices MicroPython firmware has it built in; "
+            "on CPython install pydevices-desktop and Pillow (pip install pillow)"
+        ) from None
+    w, h = fb.width, fb.height
+    if fb.format == RGB565:
+        fmt, buf = pngio.RGB565, fb.buffer
+    elif fb.format == RGB888:
+        fmt, buf = pngio.RGB888, fb.buffer
+    elif fb.format == GS8:
+        fmt, buf = pngio.GS8, fb.buffer
+    elif fb.format == MONO_HLSB:
+        # one bit a pixel, widened to grey
+        fmt, buf, row = pngio.GS8, bytearray(w * h), (w + 7) // 8
+        src = fb.buffer
+        for y in range(h):
+            for x in range(w):
+                if (src[y * row + (x >> 3)] >> (7 - (x & 7))) & 1:
+                    buf[y * w + x] = 255
+    else:
+        raise ValueError(f"PNG save not supported for format {fb.format}")
+    data = pngio.PngEncoder().encode(buf, w, h, format=fmt)
+    with open(filename, "wb") as f:
+        f.write(data)
+
+
 def save_image(fb, filename=None):
     """Save a ``FrameBuffer`` to PBM, PGM, BMP, or PNG based on format or filename.
 
@@ -83,9 +114,10 @@ def save_image(fb, filename=None):
         filename = "screenshot"
 
     file_ext = filename.rsplit(".", 1)[-1].lower() if "." in filename else None
-    if file_ext == "png":
-        with open(filename, "wb") as f:
-            write_png_file(f, fb)
+    if file_ext == "png" or fb.format == RGB888:
+        if file_ext != "png":
+            filename += ".png"
+        _save_png(fb, filename)
         return filename
 
     ext = _SAVE_FORMATS.get(fb.format)

lib/pygraphics/_framebuf_plus.py

@@ -617,16 +617,6 @@ def save(self, filename=None):
 
         return _files.save_image(self, filename)
 
-    def to_png(self):
-        """Encode this framebuffer as standard PNG bytes in memory.
-
-        Returns:
-            bytes: Complete PNG file contents.
-        """
-        from . import _png
-
-        return _png.encode_png(self)
-
     def export(self, filename):
         """Export this framebuffer as an importable ``.py`` bitmap module.
 

pygraphics.toml

@@ -14,7 +14,6 @@
 "https://raw.githubusercontent.com/PyDevices/pygraphics/main/lib/pygraphics/_font_8x16.py" = "/lib/pygraphics/_font_8x16.py"
 "https://raw.githubusercontent.com/PyDevices/pygraphics/main/lib/pygraphics/_font_8x8.py" = "/lib/pygraphics/_font_8x8.py"
 "https://raw.githubusercontent.com/PyDevices/pygraphics/main/lib/pygraphics/_framebuf_plus.py" = "/lib/pygraphics/_framebuf_plus.py"
-"https://raw.githubusercontent.com/PyDevices/pygraphics/main/lib/pygraphics/_png.py" = "/lib/pygraphics/_png.py"
 "https://raw.githubusercontent.com/PyDevices/pygraphics/main/lib/pygraphics/_shapes.py" = "/lib/pygraphics/_shapes.py"
 "https://raw.githubusercontent.com/PyDevices/pygraphics/main/lib/pygraphics/_trig.py" = "/lib/pygraphics/_trig.py"
 "https://raw.githubusercontent.com/PyDevices/pygraphics/main/lib/pygraphics/framebuf.py" = "/lib/pygraphics/framebuf.py"