/*
    This file is part of Mitsuba, a physically based rendering system.

    Copyright (c) 2007-2012 by Wenzel Jakob and others.

    Mitsuba is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License Version 3
    as published by the Free Software Foundation.

    Mitsuba is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program. If not, see <http://www.gnu.org/licenses/>.
*/

#include <mitsuba/core/statistics.h>
#include <mitsuba/core/plugin.h>
#include <mitsuba/hw/vpl.h>
#include <mitsuba/hw/session.h>
#include <mitsuba/hw/device.h>
#include <mitsuba/hw/renderer.h>
#include <mitsuba/hw/gputexture.h>

MTS_NAMESPACE_BEGIN

/*!\plugin{vpl}{Virtual Point Light integrator}
 * \order{14}
 * \parameters{
 *     \parameter{maxDepth}{\Integer}{Specifies the longest path depth
 *         in the generated output image (where \code{-1} corresponds to $\infty$).
 *	       A value of \code{2} will lead to direct-only illumination.
 *	       \default{\code{5}}
 *	   }
 *     \parameter{shadowMap\showbreak Resolution}{\Integer}{
 *       Resolution of the shadow maps that are used
 *       to compute the point-to-point visibility \default{512}
 *     }
 *     \parameter{clamping}{\Float}{
 *       A relative clamping factor between $[0,1]$ that is
 *       used to control the rendering artifact discussed below.
 *       \default{0.1}
 *     }
 * }
 *
 * This integrator implements a hardware-accelerated global illumination 
 * rendering technique based on the Instant Radiosity method by Keller 
 * \cite{Keller1997Instant}. This is the same approach that is also used in
 * Mitsuba's real-time preview; the reason for providing it as a separate
 * integrator plugin is to enable automated (e.g. scripted) usage.
 *
 * The method roughly works as follows: during a pre-process pass, any present direct 
 * and indirect illumination is converted into a set of \emph{virtual point light} 
 * sources (VPLs). The scene is then separately rendered many times, each time using 
 * a different VPL as a source of illumination. All of the renderings created in this
 * manner are accumulated to create the final output image. 
 *
 * Because the individual rendering steps can be exectuted on a
 * graphics card, it is possible to render many (i.e. 100-1000) VPLs 
 * per second. The method is not without problems, however. In particular,
 * it performs poorly when rendering glossy materials, and it produces
 * artifacts in corners and creases . Mitsuba automatically limits
 * the ``glossyness'' of materials to reduce the effects of the former
 * problem. A \code{clamping} parameter is provided to control the latter
 * (see the figure below). The number of samples per pixel specified to
 * the sampler is interpreted as the number of VPLs that should be rendered.
 *
 * \renderings{
 *     \rendering{\code{clamping=0}: With clamping fully disabled, bright
 *     blotches appear in corners and creases.}{integrator_vpl_clamping0}
 *     \rendering{\code{clamping=0.3}: Higher clamping factors remove these
 *     artifacts, but they lead to visible energy loss (the rendering
 *     is too dark in certain areas). The default of \code{0.1} is 
 *     usually reasonable.}{integrator_vpl_clamping03}
 * }
 */
class VPLIntegrator : public Integrator {
public:
	VPLIntegrator(const Properties &props) : Integrator(props) {
		/* Shadow map resolution (e.g. 512x512) */
		m_shadowMapResolution = props.getInteger("shadowMapResolution", 512);
		/* Max. depth (expressed as path length) */
		m_maxDepth = props.getInteger("maxDepth", 5);
		/* Relative clamping factor (0=no clamping, 1=full clamping) */
		m_clamping = props.getFloat("clamping", 0.1f);

		m_session = Session::create();
		m_device = Device::create(m_session);
		m_renderer = Renderer::create(m_session);
	
		m_random = new Random();
	}

	/// Draw the full scene using additive blending and shadow maps
	void drawShadowedScene(const Scene *scene, const VPL &vpl) {
		const ProjectiveCamera *sensor = static_cast<const ProjectiveCamera *>(scene->getSensor());

		Point2 aaSample = Point2(m_random->nextFloat(), m_random->nextFloat());
		Point2 apertureSample(0.5f);
		if (sensor->needsApertureSample())
			apertureSample = Point2(m_random->nextFloat(), m_random->nextFloat());

		Transform projTransform = sensor->getProjectionTransform(apertureSample, aaSample);
		Transform worldTransform = sensor->getWorldTransform()->eval(
			sensor->getShutterOpen() + 
			m_random->nextFloat() * sensor->getShutterOpenTime());
		m_shaderManager->setVPL(vpl);
		m_framebuffer->activateTarget();
		m_framebuffer->clear();
		m_renderer->setCamera(projTransform.getMatrix(), worldTransform.getInverseMatrix());
		m_shaderManager->drawAllGeometryForVPL(vpl, sensor);
		m_shaderManager->drawBackground(sensor, projTransform, vpl.emitterScale);
		m_framebuffer->releaseTarget();
	}

	bool preprocess(const Scene *scene, RenderQueue *queue, const RenderJob *job,
		int sceneResID, int sensorResID, int samplerResID) {
		Integrator::preprocess(scene, queue, job, sceneResID, sensorResID, samplerResID);

		if (!(scene->getSensor()->getType() & Sensor::EProjectiveCamera))
			Log(EError, "The VPL integrator requires a projective camera "
				"(e.g. perspective/thinlens/orthographic/telecentric)!");

		m_vpls.clear();
		size_t sampleCount = scene->getSampler()->getSampleCount();
		Float normalization = (Float) 1 / generateVPLs(scene, m_random,
				0, sampleCount, m_maxDepth, true, m_vpls);
		for (size_t i=0; i<m_vpls.size(); ++i) {
			m_vpls[i].P *= normalization;
			m_vpls[i].emitterScale *= normalization;
		}
		Log(EInfo, "Generated %i virtual point lights", m_vpls.size());

		return true;
	}

	void cancel() {
		m_cancel = true;
	}

	bool render(Scene *scene, RenderQueue *queue, 
		const RenderJob *job, int sceneResID, int sensorResID, int samplerResID) {
		ref<Sensor> sensor = scene->getSensor();
		ref<Film> film = sensor->getFilm();
		m_cancel = false;

		if (!sensor->getClass()->derivesFrom(MTS_CLASS(ProjectiveCamera)))
			Log(EError, "The VPL renderer requires a projective camera!");

		/* Initialize hardware rendering */
		m_framebuffer = m_renderer->createGPUTexture("Framebuffer", NULL);
		m_framebuffer->setFrameBufferType(GPUTexture::EColorBuffer);
		m_framebuffer->setComponentFormat(GPUTexture::EFloat32);
		m_framebuffer->setPixelFormat(GPUTexture::ERGB);
		m_framebuffer->setSize(Point3i(film->getSize().x, film->getSize().y, 1));
		m_framebuffer->setFilterType(GPUTexture::ENearest);
		m_framebuffer->setMipMapped(false);

		m_accumBuffer = m_renderer->createGPUTexture("Accumulation buffer",
			new Bitmap(Bitmap::ERGB, Bitmap::EFloat32, film->getSize()));
		m_accumBuffer->setFrameBufferType(GPUTexture::EColorBuffer);
		m_framebuffer->setComponentFormat(GPUTexture::EFloat32);
		m_framebuffer->setPixelFormat(GPUTexture::ERGB);
		m_accumBuffer->setMipMapped(false);

		MTS_AUTORELEASE_BEGIN()
		m_session->init();
		m_device->setSize(film->getSize());
		m_device->init();
		m_device->setVisible(false);
		m_renderer->init(m_device);

		if (!m_renderer->getCapabilities()->isSupported(
			RendererCapabilities::EShadingLanguage))
			Log(EError, "Support for GLSL is required!");
		if (!m_renderer->getCapabilities()->isSupported(
			RendererCapabilities::ERenderToTexture))
			Log(EError, "Render-to-texture support is required!");
		if (!m_renderer->getCapabilities()->isSupported(
			RendererCapabilities::EFloatingPointTextures))
			Log(EError, "Floating point texture support is required!");
		if (!m_renderer->getCapabilities()->isSupported(
			RendererCapabilities::EFloatingPointBuffer))
			Log(EError, "Floating point render buffer support is required!");
		if (!m_renderer->getCapabilities()->isSupported(
			RendererCapabilities::EVertexBufferObjects))
			Log(EError, "Vertex buffer object support is required!");
		if (!m_renderer->getCapabilities()->isSupported(
			RendererCapabilities::EGeometryShaders))
			Log(EError, "Geometry shader support is required!");

		/* Initialize and clear the framebuffer */
		m_framebuffer->init();
		m_accumBuffer->init();
		m_accumBuffer->activateTarget();
		m_accumBuffer->clear();
		m_accumBuffer->releaseTarget();

		m_shaderManager = new VPLShaderManager(m_renderer);
		m_shaderManager->setShadowMapResolution(m_shadowMapResolution);
		m_shaderManager->setClamping(m_clamping);
		m_shaderManager->init();
		m_shaderManager->setScene(scene);

		ProgressReporter progress("Rendering", m_vpls.size(), job);
		for (size_t i=0; i<m_vpls.size() && !m_cancel; ++i) {
			const VPL &vpl = m_vpls[i];

			m_renderer->setDepthMask(true);
			m_renderer->setDepthTest(true);
			m_renderer->setBlendMode(Renderer::EBlendNone);
			m_shaderManager->setVPL(vpl);

			m_framebuffer->activateTarget();
			m_framebuffer->clear();
			drawShadowedScene(scene, vpl);
			m_framebuffer->releaseTarget();

			m_renderer->setDepthMask(false);
			m_renderer->setDepthTest(false);
			m_renderer->setBlendMode(Renderer::EBlendAdditive);
			m_accumBuffer->activateTarget();
			m_renderer->blitTexture(m_framebuffer, true);
			m_accumBuffer->releaseTarget();

			if ((i%20) == 0) { 
				m_renderer->flush();
				m_renderer->checkError();
			}
			progress.update(i);
		}
		progress.finish();

		m_accumBuffer->download();
		film->setBitmap(m_accumBuffer->getBitmap());

		m_shaderManager->cleanup();
		m_shaderManager = NULL;

		m_framebuffer->cleanup();
		m_accumBuffer->cleanup();
		m_renderer->shutdown();
		m_device->shutdown();
		m_session->shutdown();
		MTS_AUTORELEASE_END()
		return !m_cancel;
	}

	MTS_DECLARE_CLASS()
private:
	ref<Session> m_session;
	ref<Device> m_device;
	ref<Renderer> m_renderer;
	ref<GPUTexture> m_framebuffer, m_accumBuffer;
	ref<VPLShaderManager> m_shaderManager;
	std::deque<VPL> m_vpls;
	ref<Random> m_random;
	int m_maxDepth;
	int m_shadowMapResolution;
	Float m_clamping;
	bool m_cancel;
};

MTS_IMPLEMENT_CLASS(VPLIntegrator, false, Integrator)
MTS_EXPORT_PLUGIN(VPLIntegrator, "VPL-based integrator");
MTS_NAMESPACE_END