lord help me why glsl

frontend/shader/shader.frag

@@ -0,0 +1,13 @@
+#version 300 es
+precision highp float;
+
+in vec2 vTexCoord;
+out vec4 fragColor;
+
+uniform sampler2DArray uTexArray;
+uniform int uLayer;
+
+void main() {
+    float value = texture(uTexArray, vec3(vTexCoord, float(uLayer))).r;
+    fragColor = vec4(vec3(value), 1.0);
+}