diff --git a/app/src/main/java/dk/scuffed/whiteboardapp/pipeline/stages/ChangeStage.kt b/app/src/main/java/dk/scuffed/whiteboardapp/pipeline/stages/ChangeStage.kt
new file mode 100644
index 0000000..f07e105
--- /dev/null
+++ b/app/src/main/java/dk/scuffed/whiteboardapp/pipeline/stages/ChangeStage.kt
@@ -0,0 +1,46 @@
+package dk.scuffed.whiteboardapp.pipeline.stages
+
+import android.content.Context
+import android.opengl.GLES20
+import android.util.Size
+import dk.scuffed.whiteboardapp.R
+import dk.scuffed.whiteboardapp.opengl.*
+import dk.scuffed.whiteboardapp.pipeline.*
+
+
+internal class ChangeStage(
+    context: Context,
+    private val inputFrameBufferInfo1: FramebufferInfo,
+    private val inputFrameBufferInfo2: FramebufferInfo,
+    pipeline: Pipeline): GLOutputStage(context, R.raw.vertex_shader, R.raw.change_shader, pipeline) {
+
+    init {
+        setup()
+    }
+
+    override fun setupFramebufferInfo() {
+        val resolution = Size(inputFrameBufferInfo1.textureSize.width, inputFrameBufferInfo1.textureSize.height)
+        allocateFramebuffer(GLES20.GL_RGBA, resolution)
+
+    }
+
+    override fun setupUniforms(program: Int) {
+        super.setupUniforms(program)
+
+        // Input framebuffer resolution
+        val framebufferResolutionHandle = glGetUniformLocation(program, "samplerResolution")
+        glUniform2f(framebufferResolutionHandle, inputFrameBufferInfo1.textureSize.width.toFloat(), inputFrameBufferInfo1.textureSize.height.toFloat())
+
+
+        // Input framebuffer
+        val framebufferTextureHandle1 = glGetUniformLocation(program, "sampler1")
+        glUniform1i(framebufferTextureHandle1, inputFrameBufferInfo1.textureUnitPair.textureUnitIndex)
+        glActiveTexture(inputFrameBufferInfo1.textureUnitPair.textureUnit)
+        glBindTexture(GLES20.GL_TEXTURE_2D, inputFrameBufferInfo1.textureHandle)
+
+        val framebufferTextureHandle2 = glGetUniformLocation(program, "sampler2")
+        glUniform1i(framebufferTextureHandle2, inputFrameBufferInfo2.textureUnitPair.textureUnitIndex)
+        glActiveTexture(inputFrameBufferInfo2.textureUnitPair.textureUnit)
+        glBindTexture(GLES20.GL_TEXTURE_2D, inputFrameBufferInfo2.textureHandle)
+    }
+}
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diff --git a/app/src/main/res/raw/change_shader.glsl b/app/src/main/res/raw/change_shader.glsl
new file mode 100644
index 0000000..53e095e
--- /dev/null
+++ b/app/src/main/res/raw/change_shader.glsl
@@ -0,0 +1,19 @@
+#extension GL_OES_EGL_image_external : require
+precision mediump float;
+
+uniform vec2 samplerResolution;
+uniform vec2 maskResolution;
+
+uniform sampler2D sampler1;
+uniform sampler2D sampler2;
+//uniform sampler2D mask;
+
+void main() {
+    vec2 samplersUV = gl_FragCoord.xy / samplerResolution;
+    vec2 maskUV = gl_FragCoord.xy / maskResolution;
+
+    vec4 col1 = texture2D(sampler1, samplersUV);
+    vec4 col2 = texture2D(sampler2, samplersUV);
+
+    gl_FragColor = abs(col1 - col2);
+}
\ No newline at end of file