Implement texture atlas, details on why it works unclear

shader/texture/array.frag

@@ -0,0 +1,10 @@
+#version 430 core
+in vec3 vTexPos;
+out vec4 fColor;
+
+uniform sampler2DArray tilesetSampler;
+
+void main()
+{
+    fColor = texture(tilesetSampler, vTexPos);
+}

shader/texture/array.vert

@@ -0,0 +1,12 @@
+#version 430 core
+layout (location = 0) in vec3 pos;
+layout (location = 1) in vec3 texPos;
+out vec3 vTexPos;
+
+uniform mat4 worldMat;
+
+void main()
+{
+  gl_Position = worldMat * vec4(pos,1.0) ;
+  vTexPos = texPos;
+}

shader/texture/simpleWorld.vert

@@ -7,6 +7,6 @@ uniform mat4 worldMat;
 
 void main()
 {
-  gl_Position = worldMat * vec4(pos,1);
+  gl_Position = worldMat * vec4(pos,1.0) ;
   vTexPos = texPos;
 }

shader/twoD/basic.vert

@@ -7,6 +7,6 @@ uniform mat4 worldMat;
 
 void main()
 {
-  gl_Position = worldMat * vec4(position.xyz,1);
+  gl_Position = worldMat * vec4(position,1);
   vColor = color;
 }