[rshapes] Fix multisegment Bezier splines.

[spelufo]

It seems to me that these functions are wrong, if you step the index by 1 you move to a control point instead of the next segment.

[raysan5]

@spelufo Did you test it? Could you share some code example?

[spelufo]

I did, through raylib-go:

package main

import rl "github.com/gen2brain/raylib-go/raylib"

func main() {
  rl.InitWindow(800, 600, "raylib [rshapes] example - bezier")
  defer rl.CloseWindow()

  rl.SetTargetFPS(60)

  for !rl.WindowShouldClose() {
    rl.BeginDrawing()
    rl.ClearBackground(rl.RayWhite)
    points := []rl.Vector2{
      {0.0, 0.0}, {50.0, 0.0}, {50.0, 50.0},
      {100.0, 50.0}, {100.0, 100.0}, {250.0, 250.0},
      {500.0, 500.0},
    }

    // Does the wrong thing.
    rl.DrawSplineBezierCubic(points, 5.0, rl.Green)

    // Proposed implementation:
    for i := 0; i < len(points) - 3; i += 3 {
      color := rl.Orange
      p := points[i]
      rl.DrawSplineSegmentBezierCubic(p, points[i + 1], points[i + 2], points[i + 3], 5.0, color)
    }

    rl.EndDrawing()
  }
}

[raysan5]

@spelufo I'm trying this fix with example shapes_splines_drawing, replacing current DrawSplineSegmentBezierCubic() in a loop by the proposed solution but it doesn't seem to work as expected. Please could you review it?

Drawing code I'm using:

Vector2 fullPoints[14] = {
    points[0],
    control[0].end,
    control[1].start,
    points[1],
    control[1].end,
    control[2].start,
    points[2],
    control[2].end,
    control[3].start,
    points[3],
    control[3].end,
    control[4].start,
    points[4],
    control[4].end
};

DrawSplineBezierCubic(fullPoints, 14, splineThickness, RED);

The expected result is:

[spelufo]

I've fixed the example code. I tested that the previous version of DrawSplineBezierCubic didn't work right. The new version works with this example code. The sequence of points passed to it must be points[0], control[0].start, control[0].end, points[1], ..., points[pointCount-1], and the length of control must always be pointCount - 1.

[spelufo]

Regarding the "connections", the gaps left on the points between segments, one way to cover them up would be to have DrawSplineBezierCubic draw a circle at the points connecting segments of diameter equal to the thickness of the lines. Maybe not the most efficient way to do it but it would cover the kinks.

[spelufo]

I've gone ahead and did that. It is ready to merge if you want.

[spelufo]

@raysan5 ?

[raysan5]

@spelufo Excuse the late response! I'm quite busy lately...

I want to review this code more carefully because I think the current DrawSplineSegmentBezierCubic(); implementation could not be the best one...

[colinwilcox]

Correcting the sequence of points and the iterator seems good.
I'm not sure I agree with drawing a circle in between each segment though. At the very least it should be optional and default off.

I'll take a look at the DrawSplineSegmentBezierCubic() implementation later. Do you think it is not performant?

[raysan5]

I'm not sure I agree with drawing a circle in between each segment though. At the very least it should be optional and default off.

@colinwilcox I agree, circle should be in any case, optional, I considered using a flag for it...

I'll take a look at the DrawSplineSegmentBezierCubic() implementation later. Do you think it is not performant?

DrawSplineSegmentBezierCubic(Vector2 p1, Vector2 c2, Vector2 c3, Vector2 p4, float thick, Color color);

My concerns with the function were the expected sequence of points, they should follow the pattern:

After review, it seems so. I also reviewed DrawSplineBezierCubic() and it seems it also receives and processes the lit of points as expected.

So, it seems the only issue is how shapes_splines_drawing example organizes the points to be passed to the function; that this PR seems to address.

In conclusion, raylib Cubic Bezier functions seem to be correct but the example could be confusing because it separates ControlPoints from function points for Cubic Bezier, and this is done this way because it tries to map the start-end drawing points to other spline types to be able to change between them and show a somewhat same-points curve.

Ok, I'm merging the PR and I will review it with those comments on the example.