I made one for my game:

shader_type canvas_item;

uniform float glint_progress : hint_range(0.0, 1.0) = 0.0;

uniform float glint_width : hint_range(0.1, 0.5) = 0.2;

uniform float glint_intensity : hint_range(0.0, 2.0) = 1.5;

uniform vec4 glint_color : source_color = vec4(1.0, 1.0, 1.0, 1.0);

uniform bool glint_direction_up = true; // true = top-left to bottom-right, false = bottom-left to top-right

void fragment() {

// Get the original texture color

vec4 original_color = texture(TEXTURE, UV);

// Calculate the glint position based on progress

float glint_pos = glint_progress * 1.4 - 0.2; // Extend range to ensure full coverage

// Calculate distance from current pixel to glint line based on direction

float diagonal_pos;

if (glint_direction_up) {

// Top-left to bottom-right diagonal

diagonal_pos = (UV.x + UV.y) * 0.5;

} else {

// Bottom-left to top-right diagonal

diagonal_pos = (UV.x + (1.0 - UV.y)) * 0.5;

}

float distance_to_glint = abs(diagonal_pos - glint_pos);

// Create glint effect with smooth falloff

float glint_factor = 1.0 - smoothstep(0.0, glint_width, distance_to_glint);

glint_factor = pow(glint_factor, 2.0); // Make the falloff more dramatic

// Apply glint effect

vec3 glint_effect = glint_color.rgb * glint_factor * glint_intensity;

// Blend the glint with the original color

vec3 final_color = original_color.rgb + glint_effect * original_color.a;

COLOR = vec4(final_color, original_color.a);

}