ShadowMap.h

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/* Copyright (C) 2022 Wildfire Games.
 * This file is part of 0 A.D.
 *
 * 0 A.D. is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * 0 A.D. 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 0 A.D.  If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef INCLUDED_SHADOWMAP
#define INCLUDED_SHADOWMAP

#include "renderer/backend/IDeviceCommandContext.h"
#include "renderer/backend/IShaderProgram.h"

class CBoundingBoxAligned;
class CCamera;
class CFrustum;
class CVector3D;

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.
 */
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();

    /**
     * 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);

    /**
     * Add the bounding box of an object that will cast a shadow.
     * This is used to calculate the bounds for the shadow map.
     *
     * @param bounds world space bounding box
     */
    void AddShadowCasterBound(const int cascade, const CBoundingBoxAligned& bounds);

    /**
     * Add the bounding box of an object that will receive a shadow.
     * This is used to calculate the bounds for the shadow map.
     *
     * @param bounds world space bounding box
     */
    void AddShadowReceiverBound(const CBoundingBoxAligned& bounds);

    /**
     * Compute the frustum originating at the light source, that encompasses
     * all the objects passed into AddShadowReceiverBound so far.
     *
     * This frustum can be used to determine which objects might cast a visible
     * shadow. Those objects should be passed to AddShadowCasterBound and
     * then should be rendered into the shadow map.
     */
    CFrustum GetShadowCasterCullFrustum(const int cascade);

    /**
     * Sets backend state for rendering into the shadow map texture.
     */
    void BeginRender(Renderer::Backend::IDeviceCommandContext* deviceCommandContext);

    /**
     * Finishes rendering into the shadow map.
     */
    void EndRender(Renderer::Backend::IDeviceCommandContext* deviceCommandContext);

    /**
     * Returns the current number of used cascades.
     */
    int GetCascadeCount() const;

    /**
     * Sets the renderer camera for the cascade.
     */
    void PrepareCamera(
        Renderer::Backend::IDeviceCommandContext* deviceCommandContext, const int cascade);

    /**
     * Binds all needed resources and uniforms to draw shadows using the shader.
     */
    void BindTo(
        Renderer::Backend::IDeviceCommandContext* deviceCommandContext,
        Renderer::Backend::IShaderProgram* shader) const;

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

private:
    ShadowMapInternals* m;
};

#endif // INCLUDED_SHADOWMAP