new angle and angle_rad property in vector2 #3222

AntoineMamou · 2024-11-12T17:43:12Z

This PR follows this one : #3216

I make the changes needed and add two properties :
angle_rad : Returns the vector’s angle in radians relative to the positive x-axis.
angle : Returns the angle in degrees, normalized to (180,180].

new file: test.txt

oddbookworm

Needs documentation, and there are a few issues I see offhand. But thanks for submitting! 🎉

oddbookworm · 2024-11-12T18:16:24Z

src_c/math.c

+    pgVector *vec = (pgVector *)self;
+
+    if (vec->coords[0] == 0.0 && vec->coords[1] == 0.0) {
+        return PyFloat_FromDouble(0.0);


I’d rather an exception get raised here. The zero vector is special and getting it’s angle makes no sense

ok, I thought it should be 0 because of the initial issue #3195, but I can change and raise an exception

@oddbookworm
I strongly think the angle properties should be consistent with the existing behavior of .as_polar(), .angle_to(), .rotate() and more importantly python math.atan2() (which is based off the a C standard) and polar coordinates.
These functions don't raise errors and (for not nan args) don't return nan, and most actually do not document this special case.

I still don't agree that we should silently just say the angle of the zero vector is zero. I don't like those functions treating that special case in the way they do either. And actually, the C standard does not guarantee that atan2(0, 0) returns 0. Here's a snippet from the C standard

link to standard I used

One reason I hate that behavior is because it can lead to very confusing behavior. Consider the case where you're just continuously scaling down a vector without changing it's direction. At some point, you'll go from a constant angle to 0, regardless of what the starting angle is.

Hello @aatle and @oddbookworm,
I saw on discord that there is many vision for what should be done for the zero vector. And I wanted to know if people agree on one of these in order to maybe change my code

Hi @AntoineMamou, it has been settled that we will imitate python's math.atan2() function behavior. (Returns certain value depending on sign of zeroes, for zero vector.)
See https://github.com/python/cpython/blob/ed81971e6b26c34445f06850192b34458b029337/Lib/test/test_math.py#L327 for the relevant test cases.
Here's the old CPython 3.7.2 implementation for special cases: https://github.com/python/cpython/blob/v3.7.2/Modules/mathmodule.c#L566-L600
Recent CPython relies on a library, with atan2 implemented here:
https://github.com/rust-lang/libm/blob/master/src/math/atan2.rs#L20-L31

Hi @aatle, so if we want to imitate math.atan2(), for the case where x=y=0, it should return 0, right ?

And I'm using atan2 to find the angle, so basically I can skip the if statement ?

Maybe I'm missing something here

oddbookworm · 2024-11-12T18:17:00Z

src_c/math.c

+static PyObject *
+vector_get_angle(pgVector *self, void *closure)
+{
+    pgVector *vec = (pgVector *)self;


Why this cast to the type it already is?

oddbookworm · 2024-11-12T18:17:44Z

src_c/math.c

+
+    double angle = atan2(vec->coords[1], vec->coords[0]) * 180.0 / M_PI;
+
+    if (angle > 180.0) {


Make constants instead of reusing the same hardcoded numbers

oddbookworm · 2024-11-12T18:19:02Z

src_c/math.c

+}
+
+static PyObject *
+vector_get_angle_rad(pgVector *self, void *closure)


Just reuse the function you already have instead of writing the same code twice. Since you already got the output in a form you like, just convert it from degrees to radians

oddbookworm · 2024-11-12T18:20:07Z

src_c/math.c

@@ -2585,6 +2631,8 @@ static PyMethodDef vector2_methods[] = {
 static PyGetSetDef vector2_getsets[] = {
    {"x", (getter)vector_getx, (setter)vector_setx, NULL, NULL},
    {"y", (getter)vector_gety, (setter)vector_sety, NULL, NULL},
+    {"angle", (getter)vector_get_angle, NULL, NULL, NULL},


Missing the docs component of these structs, which should be generated in the docs header, which is generated from the documentation updates you need to make

I have to make a doc in the file math.rst, right ? I'm not understanding everything about the doc yet. But I'm working on it !

…these properties

AntoineMamou · 2024-11-16T13:18:23Z

I see that two checks were not successful but I don't understand why. Can someone help me ?

aatle · 2024-11-22T06:58:02Z

buildconfig/stubs/pygame/math.pyi

+    angle: float
+    angle_rad: float


Suggested change

angle: float

angle_rad: float

@property

def angle(self) -> float: ...

@property

def angle_rad(self) -> float: ...

These are properties and they are read-only.

@property doesn't say that it's a read-only attribute, right ?

aatle · 2024-11-22T07:05:00Z

docs/reST/ref/math.rst

+      | :sl:`Gives the angle of the vector in degrees, relative to the X-axis, normalized to the interval (-180, 180].`
+
+      Read-only attribute representing the angle of the vector in degrees relative to the X-axis. This angle is normalized to
+      the interval (-180, 180].


My mistake, the interval is actually inclusive of -180. So, [-180, 180]

aatle · 2024-11-22T07:07:09Z

docs/reST/ref/math.rst

+      Read-only attribute representing the angle of the vector in degrees relative to the X-axis. This angle is normalized to
+      the interval (-180, 180].
+
+      Usage: Accessing `angle` provides the current angle of the vector in degrees within the specified range.


Reword "specified range". The word 'specified' implies that the user provides it.

aatle · 2024-11-22T07:24:49Z

src_c/math.c

+    if (angle_deg > 180.0) {
+        angle_deg -= 360.0;
+    }
+    else if (angle_deg <= -180.0) {
+        angle_deg += 360.0;
+    }


Seems unnecessary. The radians is within [-pi, pi], so the degrees will be within [-180, 180].

aatle · 2024-11-22T07:56:04Z

src_c/math.c

+}
+
+static PyObject *
+vector_get_angle_rad(pgVector *self, void *closure)


I would suggest creating a helper function _pg_atan2 that takes doubles and returns double. That way, one doesn't have to convert back to double and then to pyobject when doing more operations on it.

Where I should make the documentations for _pg_atan2 ?

aatle

LGTM.
Thanks for implementing my feature request.

Gabriele and others added 5 commits October 16, 2024 14:29

Changes to be commited:

1932b82

new file: test.txt

Delete test.txt

49dbee5

Merge branch 'pygame-community:main' into main

ddf0c48

add angle and angle_rad property for vector2

131d956

syntax error correction

91fe678

AntoineMamou requested a review from a team as a code owner November 12, 2024 17:43

oddbookworm requested changes Nov 12, 2024

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yunline added New API This pull request may need extra debate as it adds a new class or function to pygame math pygame.math labels Nov 13, 2024

code modification for properties angle and angle rad and new doc for …

faf77a8

…these properties

AntoineMamou added 4 commits November 16, 2024 15:18

type stubs correction

0f6dc9a

add new property vector2_default_angle

4d66c2a

correction math_test.py

ad6f04f

.angle and .angle_rad with math.atan2 behaviour for special cases

71c12a7

AntoineMamou requested review from oddbookworm and aatle November 19, 2024 13:45

aatle reviewed Nov 22, 2024

View reviewed changes

adding helper function _pg_atan2 + docs modification

23f426f

AntoineMamou mentioned this pull request Nov 27, 2024

New functions : Vector2.angle and Vector2.angle_rad and the tests and documentation needed #3216

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AntoineMamou requested a review from aatle November 27, 2024 10:22

aatle approved these changes Nov 30, 2024

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new angle and angle_rad property in vector2 #3222

new angle and angle_rad property in vector2 #3222

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		double angle = atan2(vec->coords[1], vec->coords[0]) * 180.0 / M_PI;

		if (angle > 180.0) {

-    angle: float
-    angle_rad: float
+    @property
+    def angle(self) -> float: ...
+    @property
+    def angle_rad(self) -> float: ...

new angle and angle_rad property in vector2 #3222

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new angle and angle_rad property in vector2 #3222

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