Camera near clipping implemented

Co-authored-by: sigonasr2 <sigonasr2@gmail.com>

main.cpp

@@ -300,6 +300,114 @@ private:
 		return v;
 	}
 	
+	vec3d Vector_IntersectPlane(vec3d &plane_p, vec3d &plane_n, vec3d &lineStart, vec3d &lineEnd)
+	{
+		plane_n = Vector_Normalise(plane_n);
+		float plane_d = -Vector_DotProduct(plane_n, plane_p);
+		float ad = Vector_DotProduct(lineStart, plane_n);
+		float bd = Vector_DotProduct(lineEnd, plane_n);
+		float t = (-plane_d - ad) / (bd - ad);
+		vec3d lineStartToEnd = Vector_Sub(lineEnd, lineStart);
+		vec3d lineToIntersect = Vector_Mul(lineStartToEnd, t);
+		return Vector_Add(lineStart, lineToIntersect);
+	}
+
+	int Triangle_ClipAgainstPlane(vec3d plane_p, vec3d plane_n, triangle &in_tri, triangle &out_tri1, triangle &out_tri2)
+	{
+		// Make sure plane normal is indeed normal
+		plane_n = Vector_Normalise(plane_n);
+
+		// Return signed shortest distance from point to plane, plane normal must be normalised
+		auto dist = [&](vec3d &p)
+		{
+			vec3d n = Vector_Normalise(p);
+			return (plane_n.x * p.x + plane_n.y * p.y + plane_n.z * p.z - Vector_DotProduct(plane_n, plane_p));
+		};
+
+		// Create two temporary storage arrays to classify points either side of plane
+		// If distance sign is positive, point lies on "inside" of plane
+		vec3d* inside_points[3];  int nInsidePointCount = 0;
+		vec3d* outside_points[3]; int nOutsidePointCount = 0;
+
+		// Get signed distance of each point in triangle to plane
+		float d0 = dist(in_tri.p[0]);
+		float d1 = dist(in_tri.p[1]);
+		float d2 = dist(in_tri.p[2]);
+
+		if (d0 >= 0) { inside_points[nInsidePointCount++] = &in_tri.p[0]; }
+		else { outside_points[nOutsidePointCount++] = &in_tri.p[0]; }
+		if (d1 >= 0) { inside_points[nInsidePointCount++] = &in_tri.p[1]; }
+		else { outside_points[nOutsidePointCount++] = &in_tri.p[1]; }
+		if (d2 >= 0) { inside_points[nInsidePointCount++] = &in_tri.p[2]; }
+		else { outside_points[nOutsidePointCount++] = &in_tri.p[2]; }
+
+		// Now classify triangle points, and break the input triangle into
+		// smaller output triangles if required. There are four possible
+		// outcomes...
+
+		if (nInsidePointCount == 0)
+		{
+			// All points lie on the outside of plane, so clip whole triangle
+			// It ceases to exist
+
+			return 0; // No returned triangles are valid
+		}
+
+		if (nInsidePointCount == 3)
+		{
+			// All points lie on the inside of plane, so do nothing
+			// and allow the triangle to simply pass through
+			out_tri1 = in_tri;
+
+			return 1; // Just the one returned original triangle is valid
+		}
+
+		if (nInsidePointCount == 1 && nOutsidePointCount == 2)
+		{
+			// Triangle should be clipped. As two points lie outside
+			// the plane, the triangle simply becomes a smaller triangle
+
+			// Copy appearance info to new triangle
+			out_tri1.col = in_tri.col;
+
+			// The inside point is valid, so keep that...
+			out_tri1.p[0] = *inside_points[0];
+
+			// but the two new points are at the locations where the
+			// original sides of the triangle (lines) intersect with the plane
+			out_tri1.p[1] = Vector_IntersectPlane(plane_p, plane_n, *inside_points[0], *outside_points[0]);
+			out_tri1.p[2] = Vector_IntersectPlane(plane_p, plane_n, *inside_points[0], *outside_points[1]);
+
+			return 1; // Return the newly formed single triangle
+		}
+
+		if (nInsidePointCount == 2 && nOutsidePointCount == 1)
+		{
+			// Triangle should be clipped. As two points lie inside the plane,
+			// the clipped triangle becomes a "quad". Fortunately, we can
+			// represent a quad with two new triangles
+
+			// Copy appearance info to new triangles
+			out_tri1.col = in_tri.col;
+			out_tri2.col = in_tri.col;
+
+			// The first triangle consists of the two inside points and a new
+			// point determined by the location where one side of the triangle
+			// intersects with the plane
+			out_tri1.p[0] = *inside_points[0];
+			out_tri1.p[1] = *inside_points[1];
+			out_tri1.p[2] = Vector_IntersectPlane(plane_p, plane_n, *inside_points[0], *outside_points[0]);
+
+			// The second triangle is composed of one of he inside points, a
+			// new point determined by the intersection of the other side of the
+			// triangle and the plane, and the newly created point above
+			out_tri2.p[0] = *inside_points[1];
+			out_tri2.p[1] = out_tri1.p[2];
+			out_tri2.p[2] = Vector_IntersectPlane(plane_p, plane_n, *inside_points[1], *outside_points[0]);
+
+			return 2; // Return two newly formed triangles which form a quad
+		}
+	}
 
 public:
 	bool OnUserCreate() override
@@ -391,37 +499,42 @@ public:
 				triViewed.p[1]=Matrix_MultiplyVector(matView,triTransformed.p[1]);
 				triViewed.p[2]=Matrix_MultiplyVector(matView,triTransformed.p[2]);
 
+				int nClippedTriangles = 0;
+				triangle clipped[2];
+				nClippedTriangles = Triangle_ClipAgainstPlane({ 0.0f, 0.0f, 0.1f }, { 0.0f, 0.0f, 1.0f }, triViewed, clipped[0], clipped[1]);
 
-				// Project triangles from 3D --> 2D
+				for (int n=0;n<nClippedTriangles;n++) {
-				triProjected.p[0]=Matrix_MultiplyVector(matProj,triViewed.p[0]);
+					// Project triangles from 3D --> 2D
-				triProjected.p[1]=Matrix_MultiplyVector(matProj,triViewed.p[1]);
+					triProjected.p[0]=Matrix_MultiplyVector(matProj,clipped[n].p[0]);
-				triProjected.p[2]=Matrix_MultiplyVector(matProj,triViewed.p[2]);
+					triProjected.p[1]=Matrix_MultiplyVector(matProj,clipped[n].p[1]);
-				triProjected.p[0]=Vector_Div(triProjected.p[0],triProjected.p[0].w);
+					triProjected.p[2]=Matrix_MultiplyVector(matProj,clipped[n].p[2]);
-				triProjected.p[1]=Vector_Div(triProjected.p[1],triProjected.p[1].w);
+					triProjected.col=triTransformed.col;
-				triProjected.p[2]=Vector_Div(triProjected.p[2],triProjected.p[2].w);
-				triProjected.col=triTransformed.col;
 
-				triProjected.p[0].x*=-1.0f;
+					triProjected.p[0]=Vector_Div(triProjected.p[0],triProjected.p[0].w);
-				triProjected.p[1].x*=-1.0f;
+					triProjected.p[1]=Vector_Div(triProjected.p[1],triProjected.p[1].w);
-				triProjected.p[2].x*=-1.0f;
+					triProjected.p[2]=Vector_Div(triProjected.p[2],triProjected.p[2].w);
-				triProjected.p[0].y*=-1.0f;
-				triProjected.p[1].y*=-1.0f;
-				triProjected.p[2].y*=-1.0f;
 
-				// Scale into view
+					triProjected.p[0].x*=-1.0f;
-				vec3d vOffsetView={1,1,0};
+					triProjected.p[1].x*=-1.0f;
-				triProjected.p[0] = Vector_Add(triProjected.p[0],vOffsetView);
+					triProjected.p[2].x*=-1.0f;
-				triProjected.p[1] = Vector_Add(triProjected.p[1],vOffsetView);
+					triProjected.p[0].y*=-1.0f;
-				triProjected.p[2] = Vector_Add(triProjected.p[2],vOffsetView);
+					triProjected.p[1].y*=-1.0f;
-				triProjected.p[0].x *= 0.5f * (float)ScreenWidth();
+					triProjected.p[2].y*=-1.0f;
-				triProjected.p[0].y *= 0.5f * (float)ScreenHeight();
-				triProjected.p[1].x *= 0.5f * (float)ScreenWidth();
-				triProjected.p[1].y *= 0.5f * (float)ScreenHeight();
-				triProjected.p[2].x *= 0.5f * (float)ScreenWidth();
-				triProjected.p[2].y *= 0.5f * (float)ScreenHeight();
 
-				vecTrianglesToRaster.push_back(triProjected);
+					// Scale into view
+					vec3d vOffsetView={1,1,0};
+					triProjected.p[0] = Vector_Add(triProjected.p[0],vOffsetView);
+					triProjected.p[1] = Vector_Add(triProjected.p[1],vOffsetView);
+					triProjected.p[2] = Vector_Add(triProjected.p[2],vOffsetView);
+					triProjected.p[0].x *= 0.5f * (float)ScreenWidth();
+					triProjected.p[0].y *= 0.5f * (float)ScreenHeight();
+					triProjected.p[1].x *= 0.5f * (float)ScreenWidth();
+					triProjected.p[1].y *= 0.5f * (float)ScreenHeight();
+					triProjected.p[2].x *= 0.5f * (float)ScreenWidth();
+					triProjected.p[2].y *= 0.5f * (float)ScreenHeight();
 
+					vecTrianglesToRaster.push_back(triProjected);
+				}
 			}
 		}
 
@@ -441,7 +554,7 @@ public:
 				{triProjected.uv[1].u,triProjected.uv[1].v},
 				{triProjected.uv[2].u,triProjected.uv[2].v},
 			},triProjected.col);
-			/*SetDecalMode(DecalMode::WIREFRAME);
+			SetDecalMode(DecalMode::WIREFRAME);
 			DrawPolygonDecal(nullptr,{
 				{triProjected.p[0].x, triProjected.p[0].y},
 				{triProjected.p[1].x, triProjected.p[1].y},
@@ -450,12 +563,12 @@ public:
 				{0,0},
 				{0,0},
 				{0,0},
-			},BLACK);*/
+			},BLACK);
 			SetDecalStructure(DecalStructure::FAN);
 		}
 
 		SetDecalMode(DecalMode::NORMAL);
-		DrawStringDecal({0,0},"Triangles: "+std::to_string(meshCube.tris.size()));
+		DrawStringDecal({0,0},"Triangles: "+std::to_string(vecTrianglesToRaster.size()));
 
 
 		return true;