OpenSpace/include/openspace/rendering/volumeraycaster.h

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 * OpenSpace                                                                             *
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 * Copyright (c) 2014-2024                                                               *
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#ifndef __OPENSPACE_CORE___VOLUMERAYCASTER___H__
#define __OPENSPACE_CORE___VOLUMERAYCASTER___H__

#include <ghoul/glm.h>
#include <filesystem>
#include <string>
#include <vector>

namespace ghoul::opengl {
    class Texture;
    class ProgramObject;
} // namespace ghoul::opengl

namespace openspace {

struct RenderData;
struct RaycastData;

class VolumeRaycaster {
public:
    /**
     * Destructor.
     */
    virtual ~VolumeRaycaster() = default;

    /**
     * Render the volume's entry points (front face of the bounding geometry).
     */
    virtual void renderEntryPoints(const RenderData& /*data*/,
        ghoul::opengl::ProgramObject& /*program*/) = 0;

    /**
     * Render the volume's exit points (back face of the bounding geometry).
     */
    virtual void renderExitPoints(const RenderData& /*data*/,
        ghoul::opengl::ProgramObject& /*program*/) = 0;

    /**
     * Prepare the volume for the ABuffer's resolve step. Make sure textures are up to
     * date, bind them to texture units, set program uniforms etc.
     */
    virtual void preRaycast(const RaycastData& data,
        ghoul::opengl::ProgramObject& program);

    /**
     * Clean up for the volume after the ABuffer's resolve step. Make sure texture units
     * are deinitialized, etc.
     */
    virtual void postRaycast(const RaycastData& data,
        ghoul::opengl::ProgramObject& program);

    /**
     * Return true if the camera is inside the volume. Also set localPosition to the
     * camera position in the volume's local coordinate system.
     */
    virtual bool isCameraInside(const RenderData& data, glm::vec3& localPosition);

    /**
     * Return a path the file to use as vertex shader.
     *
     * The shader preprocessor will have access to:
     *   - A `#{namespace}` variable (unique per helper file)
     */
    virtual std::filesystem::path boundsVertexShaderPath() const = 0;

    /**
     * Return a path to a file with the functions, uniforms and fragment shader in
     * variables required to generate the fragment color and depth.
     *
     * Should define the function: `Fragment getFragment()`
     *
     * The shader preprocessor will have access to:
     *   - A `#{namespace}` variable (unique per helper file)
     */
    virtual std::filesystem::path boundsFragmentShaderPath() const = 0;

    /**
     * Return a path to a file with all the uniforms, functions, etc. Required to perform
     * ray casting through this volume.
     *
     * The header should define the following two functions:
     * ```
     *   vec4 sample#{id}(vec3 samplePos, vec3 dir, float occludingAlpha,
     *                    inout float maxStepSize)
     *      (return color of sample)
     *   float stepSize#{id}(vec3 samplePos, vec3 dir)
     *      (return the preferred step size at this sample position)
     * ```
     *
     * The shader preprocessor will have access to:
     *   - An #{id} variable (unique per volume)
     *   - A #{namespace} variable (unique per helper file)
     */
    virtual std::filesystem::path raycasterPath() const = 0;

    /**
     * Return a path to a glsl file with helper functions required for the transformation
     * and raycast steps. This file will be included once per shader program generated,
     * regardless of how many volumes say they require the file. Ideal to avoid
     * redefinitions of helper functions.
     *
     * The shader preprocessor will have access to the #{namespace} variable (unique per
     * helper file) which should be a prefix to all symbols defined by the helper
     */
    virtual std::filesystem::path helperPath() const = 0;

    void setMaxSteps(int nsteps);

    int maxSteps() const;

    void setDownscaleRender(float value);

    float downscaleRender() const;

private:
    /// Maximum number of integration steps to be executed by the volume integrator
    int _rayCastMaxSteps = 1000;

    /// Enable and set the downscale rendering of the volume. Used to improve performance
    float _downscaleRenderConst = 1.f;
};

} // namespace openspace

#endif // __OPENSPACE_CORE___VOLUMERAYCASTER___H__