matplotlib · tacaswell · Aug 20, 2021 · Aug 15, 2021 · Aug 15, 2021 · Aug 15, 2021
diff --git a/doc/api/next_api_changes/development/20840-RJS.rst b/doc/api/next_api_changes/development/20840-RJS.rst
@@ -0,0 +1,13 @@
+Increase to minimum supported optional dependencies
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+For Matplotlib 3.5, the :ref:`minimum supported versions of optional dependencies
+<optional_dependencies>` are being bumped:
+
++------------+-----------------+---------------+
+| Dependency |  min in mpl3.4  | min in mpl3.5 |
++============+=================+===============+
+|   Tk       |      8.3        |     8.4       |
++------------+-----------------+---------------+
+
+This is consistent with our :ref:`min_deps_policy`
diff --git a/doc/devel/dependencies.rst b/doc/devel/dependencies.rst
@@ -40,7 +40,7 @@ Matplotlib figures can be rendered to various user interfaces. See
 :ref:`what-is-a-backend` for more details on the optional Matplotlib backends
 and the capabilities they provide.
 
-* Tk_ (>= 8.3, != 8.6.0 or 8.6.1) [#]_: for the Tk-based backends.
+* Tk_ (>= 8.4, != 8.6.0 or 8.6.1) [#]_: for the Tk-based backends.
 * PyQt6_ (>= 6.1), PySide6_, PyQt5_, or PySide2_: for the Qt-based backends.
 * PyGObject_: for the GTK3-based backends [#]_.
 * wxPython_ (>= 4) [#]_: for the wx-based backends.

diff --git a/lib/matplotlib/backends/_backend_tk.py b/lib/matplotlib/backends/_backend_tk.py
@@ -53,22 +53,20 @@ def _restore_foreground_window_at_end():
 # Initialize to a non-empty string that is not a Tcl command
 _blit_tcl_name = "mpl_blit_" + uuid.uuid4().hex
 
+TK_PHOTO_COMPOSITE_OVERLAY = 0  # apply transparency rules pixel-wise
+TK_PHOTO_COMPOSITE_SET = 1  # set image buffer directly
+
 
 def _blit(argsid):
     """
     Thin wrapper to blit called via tkapp.call.
 
     *argsid* is a unique string identifier to fetch the correct arguments from
     the ``_blit_args`` dict, since arguments cannot be passed directly.
-
-    photoimage blanking must occur in the same event and thread as blitting
-    to avoid flickering.
     """
-    photoimage, dataptr, offsets, bboxptr, blank = _blit_args.pop(argsid)
-    if blank:
-        photoimage.blank()
-    _tkagg.blit(
-        photoimage.tk.interpaddr(), str(photoimage), dataptr, offsets, bboxptr)
+    photoimage, dataptr, offsets, bboxptr, comp_rule = _blit_args.pop(argsid)
+    _tkagg.blit(photoimage.tk.interpaddr(), str(photoimage), dataptr,
+                comp_rule, offsets, bboxptr)
 
 
 def blit(photoimage, aggimage, offsets, bbox=None):
@@ -81,7 +79,7 @@ def blit(photoimage, aggimage, offsets, bbox=None):
     for big-endian ARGB32 (i.e. ARGB8888) data.
 
     If *bbox* is passed, it defines the region that gets blitted. That region
-    will NOT be blanked before blitting.
+    will be composed with the previous data according to the alpha channel.
 
     Tcl events must be dispatched to trigger a blit from a non-Tcl thread.
     """
@@ -95,10 +93,10 @@ def blit(photoimage, aggimage, offsets, bbox=None):
         y1 = max(math.floor(y1), 0)
         y2 = min(math.ceil(y2), height)
         bboxptr = (x1, x2, y1, y2)
-        blank = False
+        comp_rule = TK_PHOTO_COMPOSITE_OVERLAY
     else:
         bboxptr = (0, width, 0, height)
-        blank = True
+        comp_rule = TK_PHOTO_COMPOSITE_SET
 
     # NOTE: _tkagg.blit is thread unsafe and will crash the process if called
     # from a thread (GH#13293). Instead of blanking and blitting here,
@@ -107,7 +105,7 @@ def blit(photoimage, aggimage, offsets, bbox=None):
 
     # tkapp.call coerces all arguments to strings, so to avoid string parsing
     # within _blit, pack up the arguments into a global data structure.
-    args = photoimage, dataptr, offsets, bboxptr, blank
+    args = photoimage, dataptr, offsets, bboxptr, comp_rule
     # Need a unique key to avoid thread races.
     # Again, make the key a string to avoid string parsing in _blit.
     argsid = str(id(args))

diff --git a/lib/matplotlib/tests/test_backend_tk.py b/lib/matplotlib/tests/test_backend_tk.py
@@ -80,7 +80,7 @@ def test_blit():  # pragma: no cover
     for bad_box in bad_boxes:
         try:
             _tkagg.blit(
-                photoimage.tk.interpaddr(), str(photoimage), dataptr,
+                photoimage.tk.interpaddr(), str(photoimage), dataptr, 0,
                 (0, 1, 2, 3), bad_box)
         except ValueError:
             print("success")

diff --git a/src/_tkagg.cpp b/src/_tkagg.cpp
@@ -50,7 +50,7 @@ static int convert_voidptr(PyObject *obj, void *p)
 // Global vars for Tk functions.  We load these symbols from the tkinter
 // extension module or loaded Tk libraries at run-time.
 static Tk_FindPhoto_t TK_FIND_PHOTO;
-static Tk_PhotoPutBlock_NoComposite_t TK_PHOTO_PUT_BLOCK_NO_COMPOSITE;
+static Tk_PhotoPutBlock_t TK_PHOTO_PUT_BLOCK;
 #ifdef WIN32_DLL
 // Global vars for Tcl functions.  We load these symbols from the tkinter
 // extension module or loaded Tcl libraries at run-time.
@@ -63,13 +63,16 @@ static PyObject *mpl_tk_blit(PyObject *self, PyObject *args)
     char const *photo_name;
     int height, width;
     unsigned char *data_ptr;
+    int comp_rule;
+    int put_retval;
     int o0, o1, o2, o3;
     int x1, x2, y1, y2;
     Tk_PhotoHandle photo;
     Tk_PhotoImageBlock block;
-    if (!PyArg_ParseTuple(args, "O&s(iiO&)(iiii)(iiii):blit",
+    if (!PyArg_ParseTuple(args, "O&s(iiO&)i(iiii)(iiii):blit",
                           convert_voidptr, &interp, &photo_name,
                           &height, &width, convert_voidptr, &data_ptr,
+                          &comp_rule,
                           &o0, &o1, &o2, &o3,
                           &x1, &x2, &y1, &y2)) {
         goto exit;
@@ -82,7 +85,12 @@ static PyObject *mpl_tk_blit(PyObject *self, PyObject *args)
         PyErr_SetString(PyExc_ValueError, "Attempting to draw out of bounds");
         goto exit;
     }
+    if (comp_rule != TK_PHOTO_COMPOSITE_OVERLAY && comp_rule != TK_PHOTO_COMPOSITE_SET) {
+        PyErr_SetString(PyExc_ValueError, "Invalid comp_rule argument");
+        goto exit;
+    }
 
+    Py_BEGIN_ALLOW_THREADS
     block.pixelPtr = data_ptr + 4 * ((height - y2) * width + x1);
     block.width = x2 - x1;
     block.height = y2 - y1;
@@ -92,8 +100,13 @@ static PyObject *mpl_tk_blit(PyObject *self, PyObject *args)
     block.offset[1] = o1;
     block.offset[2] = o2;
     block.offset[3] = o3;
-    TK_PHOTO_PUT_BLOCK_NO_COMPOSITE(
-        photo, &block, x1, height - y2, x2 - x1, y2 - y1);
+    put_retval = TK_PHOTO_PUT_BLOCK(
+        interp, photo, &block, x1, height - y2, x2 - x1, y2 - y1, comp_rule);
+    Py_END_ALLOW_THREADS
+    if (put_retval == TCL_ERROR) {
+        return PyErr_NoMemory();
+    }
+
 exit:
     if (PyErr_Occurred()) {
         return NULL;
@@ -219,8 +232,8 @@ int load_tk(T lib)
     return
         !!(TK_FIND_PHOTO =
             (Tk_FindPhoto_t)dlsym(lib, "Tk_FindPhoto")) +
-        !!(TK_PHOTO_PUT_BLOCK_NO_COMPOSITE =
-            (Tk_PhotoPutBlock_NoComposite_t)dlsym(lib, "Tk_PhotoPutBlock_NoComposite"));
+        !!(TK_PHOTO_PUT_BLOCK =
+            (Tk_PhotoPutBlock_t)dlsym(lib, "Tk_PhotoPutBlock"));
 }
 
 #ifdef WIN32_DLL
@@ -341,8 +354,8 @@ PyMODINIT_FUNC PyInit__tkagg(void)
     } else if (!TK_FIND_PHOTO) {
         PyErr_SetString(PyExc_RuntimeError, "Failed to load Tk_FindPhoto");
         return NULL;
-    } else if (!TK_PHOTO_PUT_BLOCK_NO_COMPOSITE) {
-        PyErr_SetString(PyExc_RuntimeError, "Failed to load Tk_PhotoPutBlock_NoComposite");
+    } else if (!TK_PHOTO_PUT_BLOCK) {
+        PyErr_SetString(PyExc_RuntimeError, "Failed to load Tk_PhotoPutBlock");
         return NULL;
     }
     return PyModule_Create(&_tkagg_module);

diff --git a/src/_tkmini.h b/src/_tkmini.h
@@ -86,14 +86,19 @@ typedef struct Tk_PhotoImageBlock
     int offset[4];
 } Tk_PhotoImageBlock;
 
+#define TK_PHOTO_COMPOSITE_OVERLAY	0  // apply transparency rules pixel-wise
+#define TK_PHOTO_COMPOSITE_SET		1  // set image buffer directly
+#define TCL_OK     0
+#define TCL_ERROR  1
+
 /* Typedefs derived from function signatures in Tk header */
 /* Tk_FindPhoto typedef */
 typedef Tk_PhotoHandle (*Tk_FindPhoto_t) (Tcl_Interp *interp, const char
         *imageName);
-/* Tk_PhotoPutBLock_NoComposite typedef */
-typedef void (*Tk_PhotoPutBlock_NoComposite_t) (Tk_PhotoHandle handle,
+/* Tk_PhotoPutBLock typedef */
+typedef int (*Tk_PhotoPutBlock_t) (Tcl_Interp *interp, Tk_PhotoHandle handle,
         Tk_PhotoImageBlock *blockPtr, int x, int y,
-        int width, int height);
+        int width, int height, int compRule);
 
 #ifdef WIN32_DLL
 /* Typedefs derived from function signatures in Tcl header */