From bdf62286794e31f05fde8beb9a7152c13373e5e4 Mon Sep 17 00:00:00 2001
From: JackCarterSmith <jackcartersmith@jcsmith.fr>
Date: Sat, 28 Dec 2024 23:16:26 +0100
Subject: [PATCH] Horizon level computation final

---
 Engine/Graphics/3DRenderer.cpp | 32 +++++++++++++-------------------
 Engine/Graphics/Camera.cpp     |  1 +
 Engine/Graphics/Camera.hpp     |  4 +++-
 3 files changed, 17 insertions(+), 20 deletions(-)

diff --git a/Engine/Graphics/3DRenderer.cpp b/Engine/Graphics/3DRenderer.cpp
index bb687d3..db5ef86 100644
--- a/Engine/Graphics/3DRenderer.cpp
+++ b/Engine/Graphics/3DRenderer.cpp
@@ -58,7 +58,7 @@ Graphic3DRenderer::~Graphic3DRenderer() {}
 
 void Graphic3DRenderer::SetRTSize(unsigned int w, unsigned int h) {
     mRTSize.x = w; mRTSize.y = h;
-    mMainCamera->SetFrustrum(75.0f, mRTSize.x/mRTSize.y, 1.0f, 100.f);
+    mMainCamera->SetFrustrum(90.0f, mRTSize.x/mRTSize.y, 1.0f, 100.f);
 }
 
 void Graphic3DRenderer::UpdateCamera(CAMERA_MOVE type, const float value) {
@@ -231,29 +231,23 @@ void Graphic3DRenderer::UpdateInternalTestObjects() {
     mRenderList[2]->SetRotation(thetaAngle3, 0.f, thetaAngle3 * 0.5f);
     mRenderList[3]->SetRotation(0.f, thetaAngle, 0.f);
 }
-#include <iostream>
+
 // Compute the screen ratio between the ground and the sky (aka. Line of Horizon)
 inline float Graphic3DRenderer::ComputeSGRatio() {
     // FoV angle for Y axis is recovered using frustrum FoV and apply RT screen ratio to it
-    //const double fovYAngleDiv2 = M3D_Deg2Rad(mMainCamera->GetFoV() * mRTSize.y / mRTSize.x) * 0.5f;
-    const double fovYAngle = M3D_Deg2Rad(mMainCamera->GetFoV()) * mRTSize.y / mRTSize.x;
+    const float fovYAngleDiv2 = M3D_Deg2Rad(mMainCamera->GetFoV()) * 0.5f;
     // Get the camera pitch angle over camera FoV ratio
-    //const float theta = M3D_ScalarASin(-mMainCamera->GetLook3f().y) * (fovYAngleDiv2 + 0.2047198f) / M3D_PIDIV2;
-    const float theta = M3D_ScalarASin(-mMainCamera->GetLook3f().y);
+    const float theta = M3D_ScalarASinEst(-mMainCamera->GetLook3f().y);
+    // Get the camera altitude from the ground
+    const float altitude = mMainCamera->GetPos3f().y;
     
-    // Simple approach, real (infinite) horizon (w/o camera height and far screen calculation)
-    double sgRatio = 0.5f + std::tan(((theta / M3D_PI) / fovYAngle) * M3D_PIDIV4);
-    std::cout << (theta / M3D_PI) << ' ' << fovYAngle << ' ' << sgRatio << std::endl;
-    // Finite ground (to far plan), camera height impact the ground "level" -- KEEP FOR FURTHER USE
-    /*double sgRatio = -(mMainCamera->GetPos3f().y * 0.1f * M3D_ScalarCos(fovYAngleDiv2) - 101.f * M3D_ScalarSin(fovYAngleDiv2 + theta))
-                    / (2.f * 101.f * M3D_ScalarSin(fovYAngleDiv2) * M3D_ScalarCos(theta));
-    std::cout << fovYAngleDiv2 << ' ' << theta << ' ' << sgRatio << std::endl;*/
-    /*double p0 = 101.f / M3D_ScalarCos(fovYAngleDiv2);
-    double pf = mMainCamera->GetPos3f().y * 0.1f / M3D_ScalarSin(theta+fovYAngleDiv2);
-    double gh = (std::abs(p0 - pf) * M3D_ScalarSin(theta+fovYAngleDiv2)) / M3D_ScalarCos(theta);
-    double sh = 2.f * 101.f * std::tan(fovYAngleDiv2);
-    double sgRatio = gh / sh;
-    std::cout << fovYAngleDiv2 << ' ' << theta << " p0:" << p0 << " pf:" << pf << " gh:" << gh << " sh:" << sh << ' ' << sgRatio << std::endl;*/
+    // Ground/Sky screen ratio calculation using "simple" trigonometric properties of the
+    // pinhole (frustrum) camera model.
+    // The triangle made by the ground plane intersection with the frustum. This intersection
+    // cross the far plane at some point. Instead of computing the coordinate of the point, we
+    // directly use the far plane length to get the corresponding ratio for the screen.
+    double sgRatio = -(altitude * M3D_ScalarCosEst(fovYAngleDiv2) - mMainCamera->GetFarZ() * M3D_ScalarSinEst(fovYAngleDiv2 + theta))
+                    / (2.f * mMainCamera->GetFarZ() * M3D_ScalarSinEst(fovYAngleDiv2) * M3D_ScalarCosEst(theta));
 
     // Clamp
     if (sgRatio > 1.f)  
diff --git a/Engine/Graphics/Camera.cpp b/Engine/Graphics/Camera.cpp
index 4808206..3cd6a2c 100644
--- a/Engine/Graphics/Camera.cpp
+++ b/Engine/Graphics/Camera.cpp
@@ -8,6 +8,7 @@ Camera::Camera() {
 void Camera::SetFrustrum(float fov, float r, float zn, float zf) {
     //if (!frameDirty)
 	this->fov = fov;
+	this->zf = zf;
     M3D_MATRIX pMat = M3D_TransformMatrixFrustrumFovLH(M3D_Deg2Rad(fov), r, zn, zf);
     M3D_V4StoreF4x4(&mProjMat, pMat);
 }
diff --git a/Engine/Graphics/Camera.hpp b/Engine/Graphics/Camera.hpp
index 2d01b3f..6d83e61 100644
--- a/Engine/Graphics/Camera.hpp
+++ b/Engine/Graphics/Camera.hpp
@@ -14,6 +14,7 @@ public:
     Camera& operator= (Camera const&) = delete;
 
     float GetFoV() const { return fov; }
+    float GetFarZ() const { return zf; }
     M3D_VECTOR GetPos() const { return M3D_V4LoadF3(&mPos); }
     M3D_F3 GetPos3f() const { return mPos; }
     M3D_VECTOR GetLook() const { return M3D_V4LoadF3(&mLook); }
@@ -39,7 +40,8 @@ public:
 	void Yaw(float angle);
 
 private:
-    float fov;
+    float fov;  // It's the Y-FoV!
+    float zf;
 
     M3D_F4X4 mProjMat = M3D_MIdentity4x4();
     M3D_F4X4 mViewMat = M3D_MIdentity4x4();