ProtoTank/Engine/Graphics/3DRenderer.cpp

#include "3DRenderer.hpp"

#include "../World/DbgCube.hpp"
#include "../World/Tank.hpp"


// Rendering pipeline:
//   model matrix (Object SRT) -> view matrix (camera matrix inverted) -> proj matrix -> clipping -> perspective divide -> viewport transformation -> Rasterizer (draw pixels inside projected triangles on 2D screen)
//   object space -> world space -> camera space -> homogeneous clip space -> NDC space -> raster space
//
// Rasterizer inputs elements:
//   - texture-buffer (2D array of pixels color value)
//   - z-buffer (2D array of float representing the nearest pixel's depth, all pixels beyond are ignored)
//   - projected vertices-buffer on screen (using vertices-buffer and projection function)
//
// Refs:
//   * https://en.wikipedia.org/wiki/3D_projection
//   * https://www.scratchapixel.com/lessons/3d-basic-rendering/rasterization-practical-implementation/overview-rasterization-algorithm.html
//   * https://ktstephano.github.io/rendering/stratusgfx/aabbs
//   * https://en.wikipedia.org/wiki/Clipping_(computer_graphics)
//   * https://www.coranac.com/tonc/text/mode7.htm

Graphic3DRenderer::Graphic3DRenderer() {
    if (mMainCamera == nullptr) {
        mMainCamera = std::make_unique<Camera>();
        mMainCamera->SetPosition(0.0f, 1.5f, -8.0f);
        mMainCamera->SetFrustrum(90.0f, 1280.f/324.f, 1.0f, 100.f);
        mMainCamera->UpdateCamView();
    }

    // Fill world object list to render
    mRenderList.clear();
    mRenderList.push_back(std::make_shared<ObjectDbgCube>());
    mRenderList.back()->SetPosition(0.f, 0.f, 15.f);
    mRenderList.back()->SetScale(2.0f);
    mRenderList.push_back(std::make_shared<ObjectDbgCube>());
    mRenderList.back()->SetPosition(6.f, 2.f, 2.f);
    mRenderList.back()->SetScale(2.0f);
    mRenderList.push_back(std::make_shared<ObjectDbgCube>());
    mRenderList.back()->SetPosition(-8.f, 5.f, 10.f);
    mRenderList.back()->SetScale(2.0f);
    mRenderList.push_back(std::make_shared<Tank>());
    mRenderList.back()->SetPosition(0.f, 0.f, 0.f);
    mRenderList.back()->SetScale(5.0f);
}

Graphic3DRenderer::~Graphic3DRenderer() {}

void Graphic3DRenderer::UpdateCamera(CAMERA_MOVE type, const float value) {
    switch (type) {
    case CAMERA_MOVE_WALK:
        mMainCamera->Walk(value);
        break;

    case CAMERA_MOVE_STRAFE:
        mMainCamera->Strafe(value);
        break;

    case CAMERA_MOVE_FLY:
        mMainCamera->Fly(value);
        break;
    
    default:
        break;
    }

    mMainCamera->UpdateCamView();
}

void Graphic3DRenderer::Draw(sf::RenderTexture& context) {
    sf::BlendMode sBM = sf::BlendNone;
    sf::RenderStates sRS(sBM);

    // Hardcoded debug movement, TODO: remove it
    static float thetaAngle = 0.31f;
    thetaAngle = thetaAngle >= 6.283185f ? -6.283185f : thetaAngle + 0.004f;
    static float thetaAngle2 = 2.12f;
    thetaAngle2 = thetaAngle2 >= 6.283185f ? -6.283185f : thetaAngle2 + 0.005f;
    static float thetaAngle3 = -4.78f;
    thetaAngle3 = thetaAngle3 >= 6.283185f ? -6.283185f : thetaAngle3 + 0.008f;
    mRenderList[0]->SetRotation(thetaAngle, 0.f, thetaAngle * 0.5f);
    mRenderList[1]->SetRotation(thetaAngle2, 0.f, thetaAngle2 * 0.5f);
    mRenderList[2]->SetRotation(thetaAngle3, 0.f, thetaAngle3 * 0.5f);
    mRenderList[3]->SetRotation(0.f, thetaAngle, 0.f);
    
    M3D_MATRIX viewProjMat = mMainCamera->GetView() * mMainCamera->GetProj();
    sf::Vertex v_tri[4];

    uint32_t totVerticesCnt = 0, processedVerticesCnt = 0;
    for (auto obj : mRenderList)
        totVerticesCnt += obj->GetObjectMesh().GetVerticesCount();

    // Do the vertices projection and perspective divide
    M3D_F3 projVertices[totVerticesCnt];
    for (auto obj : mRenderList) {
        auto& oMesh = obj->GetObjectMesh();
        M3D_V3TransformPersDiv(
            projVertices + processedVerticesCnt, sizeof(M3D_F3), 
            (M3D_F3*)oMesh.vertices.data(), sizeof(Vertex), 
            oMesh.vertices.size(), 
            obj->GetTransform() * viewProjMat
        );

        //TODO: Fill a z-depth buffer...

        for (auto& objPt : obj->GetObjectMesh().parts) {
            auto indicePtr = (uint32_t*)objPt.indices.data();
            for (uint32_t i = 0; i < objPt.GetIndicesCount(); i += 3) {
                // Misscontructed indices tree failsafe
                if (i+2 > objPt.GetIndicesCount())
                    break;

                //TODO: Proceed with z-test: if z is lesser than previous z, draw the pixel and update z

                // Simple clipping
                //TODO: implement complete Cohen-Sutherland algo or similar
                if (((projVertices + processedVerticesCnt)[indicePtr[i]]).z > 0 &&
                    ((projVertices + processedVerticesCnt)[indicePtr[i+1]]).z > 0 &&
                    ((projVertices + processedVerticesCnt)[indicePtr[i+2]]).z > 0) {
                        M3D_VECTOR V1 = M3D_V4LoadF3(&(projVertices + processedVerticesCnt)[indicePtr[i]]);
                        M3D_VECTOR V2 = M3D_V4LoadF3(&(projVertices + processedVerticesCnt)[indicePtr[i+1]]);
                        M3D_VECTOR V3 = M3D_V4LoadF3(&(projVertices + processedVerticesCnt)[indicePtr[i+2]]);

                        V1 = M3D_V3TransformNDCToViewport(V1, 0.f, 0.f, 1280.f, 324.f, 1.f, 100.f);
                        V2 = M3D_V3TransformNDCToViewport(V2, 0.f, 0.f, 1280.f, 324.f, 1.f, 100.f);
                        V3 = M3D_V3TransformNDCToViewport(V3, 0.f, 0.f, 1280.f, 324.f, 1.f, 100.f);

                        v_tri[0].position = sf::Vector2f(M3D_V4GetX(V1), M3D_V4GetY(V1));
                        v_tri[0].color = oMesh.vertices[indicePtr[i]].color;
                        v_tri[3] = v_tri[0];
                        v_tri[1].position = sf::Vector2f(M3D_V4GetX(V2), M3D_V4GetY(V2));
                        v_tri[1].color = oMesh.vertices[indicePtr[i+1]].color;
                        v_tri[2].position = sf::Vector2f(M3D_V4GetX(V3), M3D_V4GetY(V3));
                        v_tri[2].color = oMesh.vertices[indicePtr[i+2]].color;
                        context.draw(v_tri, 4, sf::LineStrip, sRS);
                        //context.draw(v_tri, 3, sf::Triangles, sRS);
                }
            }
        }

        processedVerticesCnt += oMesh.GetVerticesCount();
    }
}