added proper error handling and and reflected that in the docs and tests

Author: XFajk

.my_pygame_test/main.py

@@ -10,11 +10,10 @@
 
 running = True
 while running:
-
     window.fill((255, 255, 255))
 
     pygame.draw.line(window, (255, 0, 0), l.a, l.b, 5)
-    
+
     pygame.draw.circle(window, (0, 255, 0), p, 5)
     pygame.draw.circle(window, (0, 255, 0), l.project(p, do_clamp=True), 5)
 

docs/reST/ref/geometry.rst

@@ -762,6 +762,8 @@
 
             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:: 2.5.4
 
       .. ## Line.project ##

src_c/line.c

@@ -1,6 +1,7 @@
 #include "doc/geometry_doc.h"
 #include "geometry_common.h"
 #include "methodobject.h"
+#include "pyerrors.h"
 #include "pytypedefs.h"
 
 static double
@@ -181,46 +182,6 @@ _line_scale_helper(pgLineBase *line, double factor, double origin)
     return 1;
 }
 
-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};
-
-    // 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]) /
-        (line_vector[0] * line_vector[0] + line_vector[1] * line_vector[1]);
-
-    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] >
-                 line_vector[0] * line_vector[0] +
-                     line_vector[1] * line_vector[1]) {
-            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_scale(pgLineObject *self, PyObject *const *args, Py_ssize_t nargs)
 {
@@ -261,6 +222,61 @@ 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 squred_line_length =
+        line_vector[0] * line_vector[0] + line_vector[1] * line_vector[1];
+
+    if (squred_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 (squred_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]) /
+        (line_vector[0] * line_vector[0] + line_vector[1] * line_vector[1]);
+
+    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] >
+                 line_vector[0] * line_vector[0] +
+                     line_vector[1] * line_vector[1]) {
+            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)
 {
@@ -283,13 +299,7 @@ pg_line_project(pgLineObject *self, PyObject *args, PyObject *kwnames)
                      "project requires a sequence of two numbers");
     }
 
-    PyObject *projected_point;
-    if (!(projected_point =
-              _line_project_helper(&pgLine_AsLine(self), point, clamp))) {
-        return NULL;
-    }
-
-    return projected_point;
+    return _line_project_helper(&pgLine_AsLine(self), point, clamp);
 }
 
 static struct PyMethodDef pg_line_methods[] = {

test/geometry_test.py

@@ -2208,6 +2208,9 @@ def test_meth_project(self):
         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)
@@ -2224,6 +2227,14 @@ def test_meth_project(self):
         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))"