How can i make a function graphic ?

Question

For example: do the graphic of f(x) = x^2 function

Answer 1

Here is one way to do it:

extends Node2D

func _draw():
    # Create an Expression from the formula
    var input_names = PoolStringArray(["x"])
    var expression = Expression.new()
    var err = expression.parse("sin(x)", input_names)
    if err != OK:
        print("Error parsing the formula: ", err)
        return

    # Choose graph dimensions and scales:
    # In pixels on screen
    var pixel_xmin = 0.0
    var pixel_xmax = 100.0
    var pixel_ymin = 100.0 # in Godot 2D, Y axis points down, but we want up
    var pixel_ymax = 0.0
    # Graph area
    var xmin = -4.0
    var xmax = 4.0
    var ymin = -4.0
    var ymax = 4.0

    var inputs = [0]
    var prev_pixel_y = null

    # For each pixel along the X axis
    for pixel_x in range(pixel_xmin, pixel_xmax):
        # Convert X to graph coordinates
        var x = lerp(xmin, xmax, inverse_lerp(pixel_xmin, pixel_xmax, pixel_x))

        # Execute expression
        inputs[0] = x
        var y = expression.execute(inputs)

        if expression.has_execute_failed() or is_inf(y) or is_nan(y):
            # Skip this point
            prev_pixel_y = null
            continue

        # Convert Y to graph coordinates
        var pixel_y = lerp(pixel_ymin, pixel_ymax, inverse_lerp(ymin, ymax, y))

        if prev_pixel_y != null:
            # Draw line if we have a previous value to connect to the current one
            draw_line(
                Vector2(pixel_x - 1, prev_pixel_y),
                Vector2(pixel_x, pixel_y),
                Color(1, 1, 0))

        # Remember last value so we can draw a line in the next iteration
        prev_pixel_y = pixel_y

I wrote a much more involved app in Godot to draw f(x) graphs: https://github.com/Zylann/godot_grapher

Comments

Hi

Thanks for your response.

I have gone through this earlier.

However, my need is to draw a dynamic line graph on a rectangular sprite based on a button click.

How do I achieve this ? Please help.

Thanks in advance.