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simple utility methods to make life with OpenGL core profile simpler
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/**
 * Copyright (c) 2013, Jens Hohmuth
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *  * Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *  * Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
 * THE POSSIBILITY OF SUCH DAMAGE.
 */
package de.lessvoid.coregl;

import java.nio.IntBuffer;

import de.lessvoid.coregl.spi.CoreGL;

/**
 * Helper class to use a frame buffer object. This will take care of all the
 * necessary setup. Currently this class only supports texture and not yet
 * render buffer objects.
 *
 * You're supposed to provide the actual textures an attach the textures to this
 * FBO through the methods provided on this class.
 *
 * You can enable rendering to the FBO with a call to enable() and disable it
 * again with a call to disable(). When you later want to use the textures
 * you've attached earlier you can simply bind() the original texture.
 *
 * @author void
 */
public class CoreFBO {

  private final CoreGL gl;

  private int fbo;

  CoreFBO(final CoreGL gl) {
    this.gl = gl;
    initialize();
  }

  public static CoreFBO createCoreFBO(final CoreGL gl) {
    return new CoreFBO(gl);
  }

  /**
   * Enable this FBO (glBindFramebuffer)
   */
  public void bindFramebuffer() {
    gl.glBindFramebuffer(gl.GL_FRAMEBUFFER(), fbo);
  }

  /**
   * Disable rendering to this FBO.
   */
  public void disable() {
    gl.glBindFramebuffer(gl.GL_FRAMEBUFFER(), 0);
  }

  /**
   * Disable rendering to this FBO and reset the Viewport back to screen size.
   * 
   * @param viewWidth
   *          the width to which the viewport should be reset
   * @param viewHeight
   *          the height to which the viewport should be reset
   */
  public void disableAndResetViewport(final int viewWidth, final int viewHeight) {
    gl.glBindFramebuffer(gl.GL_FRAMEBUFFER(), 0);
    gl.glViewport(0, 0, viewWidth, viewHeight);
  }

  /**
   * Delete the FBO.
   */
  public void delete() {
    gl.glDeleteFramebuffers(1, gl.getUtil().createIntBuffer(new int[] { fbo }));
  }

  /**
   * Attach a texture object to this FBO.
   *
   * @param textureId
   *          the texture to attach
   * @param colorAttachmentIdx
   *          the color attachment to use (0=GL_COLOR_ATTACHMENT0,
   *          1=GL_COLOR_ATTACHMENT1 and so on)
   */
  public void attachTexture(final int textureId, final int colorAttachmentIdx) {
    gl.glFramebufferTexture2D(gl.GL_FRAMEBUFFER(),
                              gl.GL_COLOR_ATTACHMENT0() + colorAttachmentIdx,
                              gl.GL_TEXTURE_2D(),
                              textureId,
                              0);
    gl.checkGLError("glFramebufferTexture2D");

    gl.glDrawBuffer(gl.GL_COLOR_ATTACHMENT0() + colorAttachmentIdx);
    gl.checkGLError("glDrawBuffer");

    checkFramebufferStatus();
  }

  /**
   * Attach a texture object from a texture array to this FBO.
   *
   * @param textureId
   *          the texture to attach
   * @param colorAttachmentIdx
   *          the color attachment to use (0=GL_COLOR_ATTACHMENT0,
   *          1=GL_COLOR_ATTACHMENT1 and so on)
   * @param layer
   *          the texture index inside the texture array to attach
   */
  public void attachTexture(final int textureId, final int colorAttachmentIdx, final int layer) {
    gl.glFramebufferTextureLayer(gl.GL_FRAMEBUFFER(),
                                 gl.GL_COLOR_ATTACHMENT0() + colorAttachmentIdx,
                                 textureId,
                                 0,
                                 layer);
    gl.checkGLError("glFramebufferTextureLayer");

    gl.glDrawBuffer(gl.GL_COLOR_ATTACHMENT0() + colorAttachmentIdx);
    gl.checkGLError("glDrawBuffer");

    checkFramebufferStatus();
  }

  /**
   * Attach a stencil buffer to this FBO.
   *
   * @param width
   *          the width of the stencil buffer
   * @param height
   *          the height of the stenicl buffer
   */
  public void attachStencil(final int width, final int height) {
    final IntBuffer buff = gl.getUtil().createIntBuffer(1);
    gl.glGenRenderBuffers(1, buff);
    final int renderBuffer = buff.get(0);
    gl.glBindRenderbuffer(gl.GL_RENDERBUFFER(), renderBuffer);
    gl.glRenderbufferStorage(gl.GL_RENDERBUFFER(), gl.GL_STENCIL_INDEX8(), width, height);
    gl.glFramebufferRenderbuffer(gl.GL_FRAMEBUFFER(), gl.GL_STENCIL_ATTACHMENT(), gl.GL_RENDERBUFFER(), renderBuffer);
    checkFramebufferStatus();
  }

  private void initialize() {
    final IntBuffer buffStore = gl.getUtil().createIntBuffer(1);
    gl.glGenFramebuffers(1, buffStore);
    fbo = buffStore.get(0);
    gl.checkGLError("glGenFramebuffers");
  }

  private void checkFramebufferStatus() {
    final int fboStatus = gl.glCheckFramebufferStatus(gl.GL_FRAMEBUFFER());
    if (fboStatus != gl.GL_FRAMEBUFFER_COMPLETE()) {
      throw new CoreGLException(translateErrorState(fboStatus));
    }
  }

  private String translateErrorState(final int fboStatus) {
    if (fboStatus == gl.GL_FRAMEBUFFER_UNDEFINED()) {
      return "GL_FRAMEBUFFER_UNDEFINED is returned if target is the default framebuffer, but the default framebuffer does not exist";
    } else if (fboStatus == gl.GL_FRAMEBUFFER_INCOMPLETE_ATTACHMENT()) {
      return "GL_FRAMEBUFFER_INCOMPLETE_ATTACHMENT is returned if any of the framebuffer attachment points are framebuffer incomplete.";
    } else if (fboStatus == gl.GL_FRAMEBUFFER_INCOMPLETE_MISSING_ATTACHMENT()) {
      return "GL_FRAMEBUFFER_INCOMPLETE_MISSING_ATTACHMENT is returned if the framebuffer does not have at least one image attached to it.";
    } else if (fboStatus == gl.GL_FRAMEBUFFER_INCOMPLETE_DRAW_BUFFER()) {
      return "GL_FRAMEBUFFER_INCOMPLETE_DRAW_BUFFER is returned if the value of GL_FRAMEBUFFER_ATTACHMENT_OBJECT_TYPE is GL_NONE for any color attachment point(s) named by GL_DRAWBUFFERi.";
    } else if (fboStatus == gl.GL_FRAMEBUFFER_INCOMPLETE_READ_BUFFER()) {
      return "GL_FRAMEBUFFER_INCOMPLETE_READ_BUFFER is returned if GL_READ_BUFFER is not GL_NONE and the value of GL_FRAMEBUFFER_ATTACHMENT_OBJECT_TYPE is GL_NONE for the color attachment point named by GL_READ_BUFFER.";
    } else if (fboStatus == gl.GL_FRAMEBUFFER_UNSUPPORTED()) {
      return "GL_FRAMEBUFFER_UNSUPPORTED is returned if the combination of internal formats of the attached images violates an implementation-dependent set of restrictions.";
    } else if (fboStatus == gl.GL_FRAMEBUFFER_INCOMPLETE_MULTISAMPLE()) {
      return "GL_FRAMEBUFFER_INCOMPLETE_MULTISAMPLE is returned if the value of GL_RENDERBUFFER_SAMPLES is not the same for all attached renderbuffers; if the value of GL_TEXTURE_SAMPLES is the not same for all attached textures; or, if the attached images are a mix of renderbuffers and textures, the value of GL_RENDERBUFFER_SAMPLES does not match the value of GL_TEXTURE_SAMPLES. + GL_FRAMEBUFFER_INCOMPLETE_MULTISAMPLE is also returned if the value of GL_TEXTURE_FIXED_SAMPLE_LOCATIONS is not the same for all attached textures; or, if the attached images are a mix of renderbuffers and textures, the value of GL_TEXTURE_FIXED_SAMPLE_LOCATIONS is not GL_TRUE for all attached textures.";
      // case GL_FRAMEBUFFER_INCOMPLETE_LAYER_TARGETS:
      // return "GL_FRAMEBUFFER_INCOMPLETE_LAYER_TARGETS is returned if any
      // framebuffer attachment is layered, and any populated attachment is not
      // layered, or if all populated color attachments are not from textures of
      // the same target.";
    } else {
      return "Unknown Framebuffer Status: [" + fboStatus + "]";
    }
  }
}