added webgl basics

content/Frontend/WebGL/Fragment Shaders.md

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+Fragment shaders describe ==how polygons are painted== (or textured). Read [Basics of WebGL (Drawing a Cube)](Basics%20of%20WebGL%20(Drawing%20a%20Cube).md) first.
+
+## Sample fragment vertex
+
+Parameters could be passed here as written at [Vertex Shaders](Vertex%20Shaders.md).
+
+```c
+precision highp float;
+
+// parameter from Vertex Shader
+varying vec4 v_positionWithOffset;
+// parameters passed from Javascript loop
+uniform float slide;
+uniform float aspect;
+
+void main(void){
+  // color, attached to current verticle {r,g,b,alpha}
+  // same a[
+  //   v_positionWithOffset.x,
+  //   v_positionWithOffset.y, 
+  //   v_positionWithOffset.z, 
+  //   1
+  //  ]
+  gl_FragColor=vec4(v_positionWithOffset.xyz,1);
+}```