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Sometimes the shader I am creating will be given an image file to use as a texture sampler and sometimes it will not. In the shader when the image file is given I need the line uniform sampler2D refTexture;and in the main function a line along the lines of float x = 0.5 * texture2D(refSampler, uv).rgb.x;and when no image file is given then float x = 0.5 * position.xFrom looking at the code in the samplers in the materialsLibrary I see there are some conditions on the uniforms such as #if defined(SPOTLIGHT0) || defined(DIRLIGHT0)varying vec4 vPositionFromLight0;uniform sampler2D shadowSampler0;#elseuniform samplerCube shadowSampler0;#endif1. Is there a condition I can use for #if ..................uniform sampler2D refTexture;#endif2. Is there a conditional statement within the main function I can use for IF texture loaded float x = 0.5 * texture2D(refSampler, uv).rgb.x;ELSE float x = 0.5 * position.xENDIF