Implemented the Line.project

buildconfig/stubs/pygame/geometry.pyi

@@ -197,3 +197,4 @@ class Line:
     def scale_ip(self, factor_and_origin: Point, /) -> None: ...
     def flip_ab(self) -> Line: ...
     def flip_ab_ip(self) -> None: ...
+    def project(self, point: Point, clamp: bool = False) -> tuple[float, float]: ...

docs/reST/ref/geometry.rst

@@ -740,3 +740,30 @@
          .. versionadded:: 2.5.3
 
       .. ## Line.flip_ab_ip ##
+
+   .. method:: project
+
+         | :sl:`projects the line onto the given line`
+         | :sg:`project(point: tuple[float, float], clamp=False) -> tuple[float, float]`
+
+         This method takes in a point and one boolean keyword argument clamp. It outputs an orthogonally projected point onto the line.
+         If clamp is `True` it makes sure that the outputted point will be on the line segment (which might not be orthogonal), and if it is `False` (the default) then any point on the infinitely extended line may be outputted.
+         This method can be used to find the closest point on a line to the given point. The output is the unique point on the line or line segment that is the smallest distance away from the given point.
+
+
+         .. figure:: code_examples/project.png
+            :alt: project method image
+
+            Example of how it projects the point onto the line. The red point is the point we want to project and the blue point is what you would get as a result.
+
+
+         .. figure:: code_examples/project_clamp.png
+            :alt: project clamp argument image
+
+            Example of what the clamp argument changes. If it is `True`, the point is bounded between the line segment ends.
+
+            WARNING: This method has to have some length or the clamp parameter must be true for it to work and not throw a `ValueError`
+
+         .. versionadded:: 2.5.6
+
+      .. ## Line.project ##

src_c/doc/geometry_doc.h

@@ -45,3 +45,4 @@
 #define DOC_LINE_SCALEIP "scale_ip(factor, origin) -> None\nscale_ip(factor_and_origin) -> None\nscales the line by the given factor from the given origin in place"
 #define DOC_LINE_FLIPAB "flip_ab() -> Line\nflips the line a and b points"
 #define DOC_LINE_FLIPABIP "flip_ab_ip() -> None\nflips the line a and b points, in place"
+#define DOC_LINE_PROJECT "project(point: tuple[float, float], clamp=False) -> tuple[float, float]\nprojects the line onto the given line"

src_c/line.c

@@ -219,6 +219,85 @@ pg_line_scale_ip(pgLineObject *self, PyObject *const *args, Py_ssize_t nargs)
     Py_RETURN_NONE;
 }
 
+static PyObject *
+_line_project_helper(pgLineBase *line, double *point, int clamp)
+{
+    // this is a vector that goes from one point of the line to another
+    double line_vector[2] = {line->bx - line->ax, line->by - line->ay};
+    double squared_line_length =
+        line_vector[0] * line_vector[0] + line_vector[1] * line_vector[1];
+
+    if (squared_line_length == 0.0 && clamp) {
+        double projected_point[2];
+        projected_point[0] = line->ax;
+        projected_point[1] = line->ay;
+        return pg_tuple_couple_from_values_double(projected_point[0],
+                                                  projected_point[1]);
+    }
+    else if (squared_line_length == 0.0) {
+        return RAISE(PyExc_ValueError,
+                     "The Line has to have some length or this method has to "
+                     "be clamped to work");
+    }
+
+    // this is a vector that goes from the start of the line to the point we
+    // are projecting onto the line
+    double vector_from_line_start_to_point[2] = {point[0] - line->ax,
+                                                 point[1] - line->ay};
+
+    double dot_product =
+        (vector_from_line_start_to_point[0] * line_vector[0] +
+         vector_from_line_start_to_point[1] * line_vector[1]) /
+        squared_line_length;
+
+    double projection[2] = {dot_product * line_vector[0],
+                            dot_product * line_vector[1]};
+
+    if (clamp) {
+        if (dot_product < 0) {
+            projection[0] = 0;
+            projection[1] = 0;
+        }
+        else if (projection[0] * projection[0] +
+                     projection[1] * projection[1] >
+                 squared_line_length) {
+            projection[0] = line_vector[0];
+            projection[1] = line_vector[1];
+        }
+    }
+
+    double projected_point[2] = {line->ax + projection[0],
+                                 line->ay + projection[1]};
+
+    return pg_tuple_couple_from_values_double(projected_point[0],
+                                              projected_point[1]);
+}
+
+static PyObject *
+pg_line_project(pgLineObject *self, PyObject *args, PyObject *kwnames)
+{
+    double point[2] = {0.f, 0.f};
+    int clamp = 0;
+
+    PyObject *point_obj = NULL;
+
+    static char *kwlist[] = {"point", "clamp", NULL};
+
+    if (!PyArg_ParseTupleAndKeywords(args, kwnames, "O|p:project", kwlist,
+                                     &point_obj, &clamp)) {
+        return RAISE(
+            PyExc_TypeError,
+            "project requires a sequence(point) and an optional clamp flag");
+    }
+
+    if (!pg_TwoDoublesFromObj(point_obj, &point[0], &point[1])) {
+        return RAISE(PyExc_TypeError,
+                     "project requires a sequence of two numbers");
+    }
+
+    return _line_project_helper(&pgLine_AsLine(self), point, clamp);
+}
+
 static struct PyMethodDef pg_line_methods[] = {
     {"__copy__", (PyCFunction)pg_line_copy, METH_NOARGS, DOC_LINE_COPY},
     {"copy", (PyCFunction)pg_line_copy, METH_NOARGS, DOC_LINE_COPY},
@@ -231,6 +310,8 @@ static struct PyMethodDef pg_line_methods[] = {
     {"scale", (PyCFunction)pg_line_scale, METH_FASTCALL, DOC_LINE_SCALE},
     {"scale_ip", (PyCFunction)pg_line_scale_ip, METH_FASTCALL,
      DOC_LINE_SCALEIP},
+    {"project", (PyCFunction)pg_line_project, METH_VARARGS | METH_KEYWORDS,
+     DOC_LINE_PROJECT},
     {NULL, NULL, 0, NULL}};
 
 static PyObject *

test/geometry_test.py

@@ -2201,6 +2201,40 @@ def test_meth_update(self):
         with self.assertRaises(TypeError):
             line.update(1, 2, 3)
 
+    def test_meth_project(self):
+        line = Line(0, 0, 100, 100)
+        test_point1 = (25, 75)
+        test_clamp_point1 = (100, 300)
+        test_clamp_point2 = (-50, -150)
+        test_clamp_point3 = (-200, -200)
+
+        bad_line = Line(0, 0, 0, 0)
+        test_bad_line_point = (10, 10)
+
+        projected_point = line.project(test_point1)
+        self.assertEqual(math.ceil(projected_point[0]), 50)
+        self.assertEqual(math.ceil(projected_point[1]), 50)
+
+        projected_point = line.project(test_clamp_point1, clamp=True)
+        self.assertEqual(math.ceil(projected_point[0]), 100)
+        self.assertEqual(math.ceil(projected_point[1]), 100)
+
+        projected_point = line.project(test_clamp_point2, clamp=True)
+        self.assertEqual(math.ceil(projected_point[0]), 0)
+        self.assertEqual(math.ceil(projected_point[1]), 0)
+
+        projected_point = line.project(test_clamp_point3, clamp=True)
+        self.assertEqual(math.ceil(projected_point[0]), 0)
+        self.assertEqual(math.ceil(projected_point[1]), 0)
+
+        projected_point = bad_line.project(test_bad_line_point, clamp=True)
+        self.assertEqual(math.ceil(projected_point[0]), 0)
+        self.assertEqual(math.ceil(projected_point[1]), 0)
+
+        # testing if the method fails when it should
+        with self.assertRaises(ValueError):
+            bad_line.project(test_bad_line_point)
+
     def test__str__(self):
         """Checks whether the __str__ method works correctly."""
         l_str = "Line((10.1, 10.2), (4.3, 56.4))"