// 竞技场地面网格：暗色基底 + 细网格线 + 中心放射暗角，提供空间参照与氛围
// 应用于覆盖竞技场的大 ColorRect/Polygon2D（UV 0-1 映射全幅）
shader_type canvas_item;

uniform float grid_cells = 100.0;

void fragment() {
	vec2 g = UV * grid_cells;
	vec2 f = abs(fract(g) - 0.5);
	float minor = smoothstep(0.47, 0.5, max(f.x, f.y));
	// 粗线（每 10 格）
	vec2 g2 = UV * (grid_cells / 10.0);
	vec2 f2 = abs(fract(g2) - 0.5);
	float major = smoothstep(0.46, 0.5, max(f2.x, f2.y));

	vec3 base  = vec3(0.085, 0.088, 0.115);
	vec3 minorC = vec3(0.125, 0.130, 0.165);
	vec3 majorC = vec3(0.180, 0.185, 0.240);
	vec3 col = mix(base, minorC, minor);
	col = mix(col, majorC, major);

	// 径向渐暗（边缘更暗，聚焦中心）
	float vig = 1.0 - smoothstep(0.25, 0.75, length(UV - vec2(0.5)));
	col *= mix(0.6, 1.15, vig);
	COLOR = vec4(col, 1.0);
}