/**
 * =========================================================================
 * File        : ShadowMap.h
 * Project     : Pyrogenesis
 * Description : Shadow mapping related texture and matrix management
 *
 * @author Nicolai Hähnle <nicolai@wildfiregames.com>
 * =========================================================================
 */

#ifndef SHADOWMAP_H
#define SHADOWMAP_H

#include "lib/ogl.h"

class CBound;
class CMatrix3D;

struct ShadowMapInternals;

/**
 * Class ShadowMap: Maintain the shadow map texture and perform necessary OpenGL setup,
 * including matrix calculations.
 *
 * The class will automatically generate a texture the first time the shadow map is rendered into.
 * The texture will not be resized afterwards.
 *
 * Can use a simple luminance map to store shadows (no self-shadowing possible) or
 * depth textures (with self-shadowing). Default is to use a luminance map, use SetUseDepthTexture
 * to override the default.
 */
class ShadowMap
{
public:
	ShadowMap();
	~ShadowMap();

	/**
	 * RecreateTexture: Destroy the current shadow texture and force creation of
	 * a new one. Useful when the renderer's size has changed and the texture
	 * should be resized too.
	 */
	void RecreateTexture();

	/**
	 * GetUseDepthTexture: Return whether rendering uses a depth texture (instead of
	 * a luminance texture).
	 *
	 * Note that this value may be changed automatically based on OpenGL capabilities.
	 * It is guarantueed that it stays constant after SetupFrame until the end of the
	 * frame or the next call to SetUseDepthTexture.
	 *
	 * @return whether shadow rendering uses depth textures
	 */
	bool GetUseDepthTexture() const;

	/**
	 * SetUseDepthTexture: Set whether shadowing should use depth textures.
	 * Note that even passing @c true for depthTexture does not actually guarantuee that
	 * depth textures will be used (mostly due to OpenGL capabilities). See the comment
	 * for GetUseDepthTexture.
	 *
	 * @param depthTexture whether shadow rendering should use depth textures
	 */
	void SetUseDepthTexture(bool depthTexture);

	/**
	 * GetDepthTextureBits: Return the number of bits to use for depth textures when
	 * enabled.
	 *
	 * @return depth texture bit depth
	 */
	int GetDepthTextureBits() const;

	/**
	 * SetDepthTextureBits: Sets the number of bits to use for depth textures when enabled.
	 * Possible values are 16, 24, 32 and 0 (= use default)
	 *
	 * @param bits number of bits
	 */
	void SetDepthTextureBits(int bits);

	/**
	 * SetupFrame: Configure light space for the given camera and light direction,
	 * create the shadow texture if necessary, etc.
	 *
	 * @param camera the camera that will be used for world rendering
	 * @param lightdir the direction of the (directional) sunlight
	 */
	void SetupFrame(const CCamera& camera, const CVector3D& lightdir);

	/**
	 * AddShadowedBound: Add the bounding box of an object that has to be shadowed.
	 * This is used to calculate the bounds for the shadow map.
	 *
	 * @param bounds world space bounding box
	 */
	void AddShadowedBound(const CBound& bounds);

	/**
	 * BeginRender: Set OpenGL state for rendering into the shadow map texture.
	 *
	 * @todo this depends in non-obvious ways on the behaviour of the call-site
	 */
	void BeginRender();

	/**
	 * EndRender: Finish rendering into the shadow map.
	 *
	 * @todo this depends in non-obvious ways on the behaviour of the call-site
	 */
	void EndRender();

	/**
	 * GetTexture: Retrieve the OpenGL texture object name that contains the shadow map.
	 *
	 * @return the texture name of the shadow map texture
	 */
	GLuint GetTexture() const;

	/**
	 * GetTextureMatrix: Retrieve the world-space to shadow map texture coordinates
	 * transformation matrix.
	 *
	 * @return the matrix that transforms world-space coordinates into homogenous
	 * shadow map texture coordinates
	 */
	const CMatrix3D& GetTextureMatrix() const;

	/**
	 * RenderDebugDisplay: Visualize shadow mapping calculations to help in
	 * debugging and optimal shadow map usage.
	 */
	void RenderDebugDisplay();

private:
	ShadowMapInternals* m;
};

#endif // SHADOWMAP_H
