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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[Bug]: FigureCanvasTkAgg renders clipped/oversized when embedded in layout-managed container on Windows HiDPI","articleBody":"### Bug summary\n\nWhen `FigureCanvasTkAgg` is embedded in a layout-managed container (e.g., a `Frame` with `pack(fill=BOTH, expand=True)`), the plot is rendered larger than the visible canvas area on Windows with HiDPI display scaling (\u003e100%). The right and bottom portions of the figure are clipped/cropped.\n\nThe root cause is in `FigureCanvasTk._update_device_pixel_ratio()`: it updates `figure.dpi` via `_set_device_pixel_ratio()` and then calls `self._tkcanvas.configure(width=physical_w, height=physical_h)`. When the canvas is constrained by a geometry manager (`pack`/`grid`), the actual displayed size does not change, so `\u003cConfigure\u003e` does not fire, and `resize()` is never called to recalculate `figure.size_inches` with the new DPI. This results in a render buffer that is `device_pixel_ratio` times larger than the visible area.\n\n### Code for reproduction\n\n```Python\n\"\"\"\nRun on Windows with display scaling \u003e 100%.\nExpected: Plot fills the visible canvas area correctly.\nActual: Plot is rendered larger than visible area; right/bottom portions are clipped.\n\"\"\"\nimport ctypes\nimport tkinter as tk\nimport numpy as np\nfrom matplotlib.figure import Figure\nfrom matplotlib.backends.backend_tkagg import FigureCanvasTkAgg\n\n# Standard Windows HiDPI setup\nctypes.windll.shcore.SetProcessDpiAwareness(1)\n\nroot = tk.Tk()\nroot.geometry(\"800x600\")\n\nframe = tk.Frame(root)\nframe.pack(fill=tk.BOTH, expand=True)\n\nfig = Figure(dpi=96)\nax = fig.add_subplot(111)\nx = np.linspace(0, 2 * np.pi, 100)\nax.plot(x, np.sin(x), label=\"sin(x)\")\nax.plot(x, np.cos(x), label=\"cos(x)\")\nax.set_xlabel(\"X Axis - may be clipped\")\nax.set_ylabel(\"Y Axis - may be clipped\")\nax.set_title(\"Embedded FigureCanvasTkAgg - HiDPI clipping bug\")\nax.legend()\nax.grid(True)\nfig.tight_layout()\n\ncanvas = FigureCanvasTkAgg(fig, master=frame)\ncanvas.get_tk_widget().pack(fill=tk.BOTH, expand=True)\n\n# Diagnostic output\ndef diagnostics(event=None):\n    w = canvas.get_tk_widget()\n    cfg_w, cfg_h = int(w[\"width\"]), int(w[\"height\"])\n    act_w, act_h = w.winfo_width(), w.winfo_height()\n    sz = fig.get_size_inches()\n    render_w, render_h = int(sz[0] * fig.dpi), int(sz[1] * fig.dpi)\n    print(f\"device_pixel_ratio: {canvas.device_pixel_ratio}\")\n    print(f\"figure.dpi: {fig.dpi} (original: {fig._original_dpi})\")\n    print(f\"figure.get_size_inches(): [{sz[0]:.2f}, {sz[1]:.2f}]\")\n    print(f\"Render size: {render_w}x{render_h}\")\n    print(f\"Canvas configured: {cfg_w}x{cfg_h}\")\n    print(f\"Canvas actual:     {act_w}x{act_h}\")\n    if render_w != act_w or render_h != act_h:\n        print(f\"BUG: render size ({render_w}x{render_h}) != \"\n              f\"actual size ({act_w}x{act_h})\")\n\nroot.after(500, diagnostics)\ncanvas.draw()\nroot.mainloop()\n```\n\n### Actual outcome\n\nOn Windows 11 with 150% display scaling:\n\n```\ndevice_pixel_ratio: 1.5\nfigure.dpi: 144.0 (original: 96)\nfigure.get_size_inches(): [8.33, 6.25]\nRender size: 1200x900\nCanvas configured: 1200x900\nCanvas actual:     800x600\nBUG: render size (1200x900) != actual size (800x600)\n```\n\nThe plot is rendered at 1200×900 pixels but only 800×600 pixels are visible. The bottom and right portions (axis labels, legend, etc.) are cropped.\n\nNote: this also reproduces **without** manually setting `tk scaling` — just `SetProcessDpiAwareness(1)` is sufficient, because Tk automatically adjusts its scaling factor on HiDPI displays, and `_update_device_pixel_ratio` reads it.\n\n### Expected outcome\n\nThe plot should be fully visible within the canvas area with no clipping, regardless of the display scaling factor. The render size should match the actual displayed size.\n\n### Additional information\n\nThe chain of events:\n\n1. Canvas is packed → `\u003cConfigure\u003e` fires with actual size (800×600) → `resize()` sets `figure.size_inches = (800/96, 600/96) = (8.33, 6.25)`\n2. Canvas becomes visible → `\u003cMap\u003e` fires → `_update_device_pixel_ratio()` runs\n3. `_set_device_pixel_ratio(1.5)` changes `figure.dpi` from 96 to 144\n4. `configure(width=1200, height=900)` sets the canvas **requested** size\n5. `pack(fill=BOTH, expand=True)` constrains the **actual** size to 800×600\n6. Since actual size didn't change, `\u003cConfigure\u003e` does NOT fire\n7. `figure.size_inches` is still `(8.33, 6.25)` (calculated with the old dpi=96)\n8. Render size = `size_inches × new_dpi = (8.33×144, 6.25×144) = (1200, 900)`\n9. But only 800×600 is visible → **right and bottom portions are clipped**\n\nThis works correctly in `FigureManagerTk` (matplotlib's own window) because the canvas is packed directly in the top-level window, and `configure()` causes the window to resize, which triggers `\u003cConfigure\u003e` → `resize()`. But when the canvas is embedded in a user-managed layout, the geometry manager constrains the size and `\u003cConfigure\u003e` may not fire.\n\n### Suggested fix \n\nAfter `_set_device_pixel_ratio` changes the DPI and `configure` sets the new requested size, `_update_device_pixel_ratio` should ensure `resize()` is called even if `\u003cConfigure\u003e` doesn't fire. For example:\n\n```python\ndef _update_device_pixel_ratio(self, event=None):\n    ratio = None\n    if sys.platform == 'win32':\n        ratio = round(self._tkcanvas.tk.call('tk', 'scaling') / (96 / 72), 2)\n    elif sys.platform == \"linux\":\n        ratio = self._tkcanvas.winfo_fpixels('1i') / 96\n    if ratio is not None and self._set_device_pixel_ratio(ratio):\n        w, h = self.get_width_height(physical=True)\n        self._tkcanvas.configure(width=w, height=h)\n        # If the actual displayed size is constrained by a layout manager\n        # and didn't change, \u003cConfigure\u003e won't fire and resize() won't run.\n        # Force a resize to recalculate figure.size_inches with the new DPI.\n        self._tkcanvas.update_idletasks()\n        actual_w = self._tkcanvas.winfo_width()\n        actual_h = self._tkcanvas.winfo_height()\n        if actual_w \u003e 0 and actual_h \u003e 0 and (actual_w != w or actual_h != h):\n            self.resize(type('Event', (), {'width': actual_w, 'height': actual_h})())\n```\n\n### Operating system\n\nWindows 11 (10.0.26200)\n\n### Matplotlib Version\n\n3.10.7 \n\n### Matplotlib Backend\n\nTkAgg\n\n### Python version\n\n3.12.12\n\n### Jupyter version\n\n_No response_\n\n### Installation\n\nconda","author":{"url":"https://github.com/lzz8246","@type":"Person","name":"lzz8246"},"datePublished":"2026-02-10T06:53:11.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":5},"url":"https://github.com/31126/matplotlib/issues/31126"}