/*
 * Copyright 2016 MovingBlocks
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.terasology.rendering.dag.nodes;

import org.terasology.assets.ResourceUrn;
import org.terasology.monitoring.PerformanceMonitor;
import org.terasology.rendering.assets.material.Material;
import org.terasology.rendering.dag.ConditionDependentNode;
import org.terasology.rendering.dag.stateChanges.BindFBO;
import org.terasology.rendering.dag.stateChanges.EnableMaterial;
import org.terasology.rendering.dag.stateChanges.SetViewportToSizeOf;
import org.terasology.rendering.opengl.BaseFBOsManager;
import org.terasology.rendering.opengl.FBO;
import org.terasology.rendering.opengl.FBOConfig;
import org.terasology.rendering.opengl.FBOManagerSubscriber;

import static org.terasology.rendering.opengl.OpenGLUtils.renderFullscreenQuad;

/**
 * A BlurNode takes the content of the color buffer attached to the input FBO and generates
 * a blurred version of it in the color buffer attached to the output FBO.
 */
public class BlurNode extends ConditionDependentNode implements FBOManagerSubscriber {

    protected float blurRadius;

    private Material blurMaterial;
    private String performanceMonitorLabel;

    private BaseFBOsManager fboManager;

    private FBOConfig inputFBOConfig;
    private FBOConfig outputFBOConfig;

    private FBO inputFBO;
    private FBO outputFBO;

    /**
     * Throws a RuntimeException if invoked. Use initialise(...) instead.
     */
    @Override
    public void initialise() {
        throw new RuntimeException("Please do not use initialise(). For this class use initialise(...) instead.");
    }

    /**
     * Initializes the BlurNode instance.
     *
     * @param inputConfig an FBOConfig instance describing the input FBO, to be retrieved from the FBO manager
     * @param outputConfig an FBOConfig instance describing the output FBO, to be retrieved from the FBO manager
     * @param anfboManager the FBO manager from which to retrieve -both- FBOs.
     * @param aRadius the blur radius: higher values cause higher blur. The shader's default is 16.0f.
     * @param aLabel a String to label the instance's entry in output generated by the PerformanceMonitor
     */
    public void initialise(FBOConfig inputConfig, FBOConfig outputConfig, BaseFBOsManager anfboManager, float aRadius, String aLabel) {

        this.inputFBOConfig = inputConfig;
        this.outputFBOConfig = outputConfig;
        this.fboManager = anfboManager;

        requiresFBO(inputFBOConfig, fboManager);
        requiresFBO(outputFBOConfig, fboManager);
        addDesiredStateChange(new BindFBO(outputFBOConfig.getName(), fboManager));
        addDesiredStateChange(new SetViewportToSizeOf(outputFBOConfig.getName(), fboManager));

        inputFBO = fboManager.get(inputFBOConfig.getName());
        outputFBO = fboManager.get(outputFBOConfig.getName());
        fboManager.subscribe(this);

        setupConditions();

        addDesiredStateChange(new EnableMaterial("engine:prog.blur"));
        this.blurMaterial = getMaterial(new ResourceUrn("engine:prog.blur"));

        this.blurRadius = aRadius;
        this.performanceMonitorLabel = aLabel;
    }

    /**
     * This method does nothing. It is meant to be overridden by inheriting classes if needed.
     * On the other hand, there might be situations in which the blur should always occur,
     * in which case this BlurNode class is good as it is.
     */
    protected void setupConditions() { }

    /**
     * Performs the blur.
     */
    @Override
    public void process() {
        PerformanceMonitor.startActivity("rendering/" + performanceMonitorLabel);

        // TODO: these shader-related operations should go in their own StateChange implementations
        blurMaterial.setFloat("radius", blurRadius, true);
        blurMaterial.setFloat2("texelSize", 1.0f / outputFBO.width(), 1.0f / outputFBO.height(), true);

        // TODO: binding the color buffer of an FBO should also be done in its own StateChange implementation
        inputFBO.bindTexture();

        renderFullscreenQuad();

        PerformanceMonitor.endActivity();
    }

    @Override
    public void update() {
        inputFBO = fboManager.get(inputFBOConfig.getName());
        outputFBO = fboManager.get(outputFBOConfig.getName());
    }

}