How to use sin wave in shader

Godot Version

4.2.2

Question

my code

shader_type canvas_item;
varying float depth;
// uniform vec4 color;
uniform float frequency = 0.1;

void vertex() {
	// Called for every vertex the material is visible on.
	depth = (sin(10.0*VERTEX.x)+1.0)/2.0;
}

void fragment() {
	// Called for every pixel the material is visible on.
	vec4 pixelColor = texture(TEXTURE,UV);
	pixelColor.a = depth;
	COLOR = pixelColor;
}

//void light() {
	// Called for every pixel for every light affecting the CanvasItem.
	// Uncomment to replace the default light processing function with this one.
//}

I expect this to form a sinwave like structure but why it giving a gradient?

Note: Vertex.x ranges from 0 to 1 since i made the size as 1 and increased the scale factor accordingly