OpenSpace/modules/globebrowsing/meshes/skirtedgrid.cpp

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 * OpenSpace                                                                             *
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 * Copyright (c) 2014-2018                                                               *
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#include <modules/globebrowsing/meshes/skirtedgrid.h>

#include <ghoul/misc/assert.h>

namespace {
    size_t numElements(int xSegments, int ySegments) {
        return 3 * 2 * xSegments * ySegments;
    }

    size_t numVertices(int xSegments, int ySegments) {
        return (xSegments + 1) * (ySegments + 1);
    }

    void validate([[maybe_unused]] int xSegments, [[maybe_unused]] int ySegments) {
        ghoul_assert(
            xSegments > 0 && ySegments > 0,
            "Resolution must be at least 1x1. (" + std::to_string(xSegments) + ", " +
            std::to_string(ySegments) + ")"
        );
    }
} // namespace

namespace openspace::globebrowsing {

SkirtedGrid::SkirtedGrid(unsigned int xSegments, unsigned int ySegments,
                         TriangleSoup::Positions usePositions,
                         TriangleSoup::TextureCoordinates useTextureCoordinates,
                         TriangleSoup::Normals useNormals)
    : Grid(xSegments, ySegments)
{
    _geometry = std::make_unique<TriangleSoup>(
        createElements(xSegments, ySegments),
        usePositions,
        useTextureCoordinates,
        useNormals
    );

    if (usePositions) {
        _geometry->setVertexPositions(createPositions(_xSegments, _ySegments));
    }
    if (useTextureCoordinates) {
        _geometry->setVertexTextureCoordinates(
            createTextureCoordinates(_xSegments, _ySegments)
        );
    }
    if (useNormals) {
        _geometry->setVertexNormals(createNormals(_xSegments, _ySegments));
    }
}

int SkirtedGrid::xSegments() const {
    return _xSegments;
}

int SkirtedGrid::ySegments() const {
    return _ySegments;
}

std::vector<GLuint> SkirtedGrid::createElements(int xSegments, int ySegments) {
    validate(xSegments, ySegments);

    std::vector<GLuint> elements;
    elements.reserve(numElements(xSegments + 2, ySegments + 2));
    for (int y = 0; y < ySegments + 2; y++) {
        for (int x = 0; x < xSegments + 2; x++) {

            // x    v01---v11   x ..
            //       |  /  |
            // x    v00---v10   x ..
            //
            // x    x     x     x ..
            // :    :     :     :

            const GLuint v00 = (y + 0) * (xSegments + 2 + 1) + x + 0;
            const GLuint v10 = (y + 0) * (xSegments + 2 + 1) + x + 1;
            const GLuint v01 = (y + 1) * (xSegments + 2 + 1) + x + 0;
            const GLuint v11 = (y + 1) * (xSegments + 2 + 1) + x + 1;

            // add upper triangle
            elements.push_back(v00);
            elements.push_back(v10);
            elements.push_back(v11);

            // add lower triangle
            elements.push_back(v00);
            elements.push_back(v11);
            elements.push_back(v01);
        }
    }

    return elements;
}

std::vector<glm::vec4> SkirtedGrid::createPositions(int xSegments, int ySegments) {
    validate(xSegments, ySegments);

    // Copy from 2d texture coordinates and use as template to create positions
    const std::vector<glm::vec2>& templateTextureCoords = createTextureCoordinates(
        xSegments,
        ySegments
    );

    std::vector<glm::vec4> positions;
    positions.reserve(numVertices(xSegments, ySegments));
    for (const glm::vec2& c : templateTextureCoords) {
        positions.emplace_back(c, 0.f, 1.f);
    }
    return positions;
}

std::vector<glm::vec2> SkirtedGrid::createTextureCoordinates(int xSegments, int ySegments)
{
    validate(xSegments, ySegments);

    std::vector<glm::vec2> textureCoordinates;
    textureCoordinates.reserve(numVertices(xSegments + 2, ySegments + 2));
    for (int y = -1; y < ySegments + 2; y++) {
        for (int x = -1; x < xSegments + 2; x++) {
            textureCoordinates.emplace_back(
                glm::clamp(
                    static_cast<float>(x) / static_cast<float>(xSegments),
                    0 - 1.f / (2 * xSegments),
                    1 + 1.f / (2 * xSegments)
                ),
                glm::clamp(
                    static_cast<float>(y) / static_cast<float>(ySegments),
                    0 - 1.f / (2 * ySegments),
                    1 + 1.f / (2 * ySegments)
                )
            );
        }
    }
    return textureCoordinates;
}

std::vector<glm::vec3> SkirtedGrid::createNormals(int xSegments, int ySegments) {
    validate(xSegments, ySegments);

    std::vector<glm::vec3> normals;
    normals.reserve(numVertices(xSegments + 2, ySegments + 2));
    for (int y = -1; y < ySegments + 2; y++) {
        for (int x = -1; x < xSegments + 2; x++) {
            normals.emplace_back(0.f, 0.f, 1.f);
        }
    }

    return normals;
}

} // namespace openspace::globebrowsing