Additional resources from the Raylib repo.

Examples/resources/shaders/glsl120/wave.fs

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+#version 120
+
+// Input vertex attributes (from vertex shader)
+varying vec2 fragTexCoord;
+varying vec4 fragColor;
+
+// Input uniform values
+uniform sampler2D texture0;
+uniform vec4 colDiffuse;
+
+uniform float seconds;
+uniform vec2 size;
+uniform float freqX;
+uniform float freqY;
+uniform float ampX;
+uniform float ampY;
+uniform float speedX;
+uniform float speedY;
+
+void main()
+{
+    float pixelWidth = 1.0/size.x;
+    float pixelHeight = 1.0/size.y;
+    float aspect = pixelHeight/pixelWidth;
+    float boxLeft = 0.0;
+    float boxTop = 0.0;
+
+    vec2 p = fragTexCoord;
+    p.x += cos((fragTexCoord.y - boxTop)*freqX/(pixelWidth*750.0) + (seconds*speedX))*ampX*pixelWidth;
+    p.y += sin((fragTexCoord.x - boxLeft)*freqY*aspect/(pixelHeight*750.0) + (seconds*speedY))*ampY*pixelHeight;
+
+    gl_FragColor = texture2D(texture0, p)*colDiffuse*fragColor;
+}