Set up a multipass shader

assets/shared/shaders/test.frag

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+#version 330 core
+
+in vec2 TexCoord;
+uniform sampler2D u_Text0;
+uniform sampler2D u_Text1;
+out vec4 FragColor;
+
+void main() {
+  vec4 color1 = texture(u_Text0, TexCoord);
+  vec4 color2 = texture(u_Text1, TexCoord);
+  FragColor = color1 * color2.r;
+}

assets/shared/shaders/test.vert

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+#version 300 es
+#ifdef GL_ES
+  
+#else
+  #extension GL_ARB_separate_shader_objects : enable
+#endif
+
+layout (location = 0) in vec3 aPos;
+layout (location = 1) in vec2 aTexCoord;
+
+uniform mat4 u_Proj;
+uniform mat4 u_View;
+uniform mat4 u_Modl;
+
+out vec2 TexCoord;
+
+void main() {
+  gl_Position = u_Proj * u_View * u_Modl * vec4(aPos, 1.0);
+  TexCoord = vec2(aTexCoord.x, aTexCoord.y);
+}