raylib: [raymath] Vector2LineAngle() may be giving wrong results

As far as I am aware I have done the following:

• I tested it on latest raylib version from master branch
• I checked there is no similar issue already reported
• I checked the documentation on the wiki
• My code has no errors or misuse of raylib

Issue description

Vector2Angle and Vector2LineAngle give results of different signedness. This might be intended behavior but I wasn’t sure.

After looking at some other functions that use angles (Vector2Rotate() and DrawCircleSector()) it seems raylib has a clockwise bias for angles, so I am inclined to think that Vector2Angle() has the correct result of the two.

Issue Screenshot

Solution

In raymath.h, Simply changing “atan2f” in Vector2LineAngle() to “-atan2f” should fix the issue.

Code Example

You can test the behavior with the following program:

#include "raylib.h"

#include "raymath.h"

int main(void){

    int screenWidth = 800;
    int screenHeight = 450;

    InitWindow(screenWidth, screenHeight, "Vector Angle Test");
    SetTargetFPS(60);

    Vector2 vOrigin = { (float)screenWidth/2.0f, (float)screenHeight/2.0f };
    Vector2 v1 = Vector2Add(vOrigin, (Vector2){100.0f, 0.0f});
    Vector2 v2 = Vector2Add(vOrigin, (Vector2){-100.0f, 80.0f}); 
    int v2Flipped = 0;

    float angleVector;
    float angleLine; 

    while(!WindowShouldClose()){

        if (v2Flipped && IsKeyPressed(KEY_SPACE))
        {
            v2 = Vector2Add(vOrigin, (Vector2){-100.0f, 80.0f});
            v2Flipped = 0;
        } 
        else if (IsKeyPressed(KEY_SPACE))
        {
            v2 = Vector2Add(vOrigin, (Vector2){-100.0f, -80.0f});
            v2Flipped = 1;
        }

        Vector2 v1Normal = Vector2Normalize(Vector2Subtract(v1, vOrigin));
        Vector2 v2Normal = Vector2Normalize(Vector2Subtract(v2, vOrigin));

        angleVector = Vector2Angle(v1Normal, v2Normal)*RAD2DEG;
        angleLine = Vector2LineAngle(vOrigin, v2)*RAD2DEG;

        BeginDrawing();

            ClearBackground(RAYWHITE);

            DrawText(TextFormat("ANGLE VECTOR: %3.2f", angleVector), 20, 20, 20.0f, BLACK);
            DrawText(TextFormat("ANGLE LINE: %3.2f", angleLine), 20, 40, 20.0f, BLACK);

            DrawLineEx(vOrigin, v1, 3.0f, BLACK);
            DrawLineEx(vOrigin, v2, 3.0f, BLACK);

            DrawCircleV(vOrigin, 5.0f, LIME);
            DrawCircleV(v1, 5.0f, BLUE);
            DrawCircleV(v2, 5.0f, RED);

            DrawText("vOrigin", vOrigin.x, vOrigin.y+10, 10.0f, DARKGRAY);
            DrawText("v1", v1.x+10, v1.y, 10.0f, DARKGRAY);
            DrawText("v2", v2.x-20, v2.y, 10.0f, DARKGRAY);

        EndDrawing();

    }

    CloseWindow();

}

Apologies if this is painfully bad, it’s my first time submitting an issue.