From 9992d36bf356d158a43af3a95b7c817587e5997f Mon Sep 17 00:00:00 2001
From: Nev3r <apophycens@gmail.com>
Date: Wed, 2 Jun 2021 10:58:36 +0200
Subject: [PATCH] Add slope equation constant parsing functionality.

---
 src/p_slopes.c | 40 ++++++++++++++++++++++++++++++++++++++++
 src/p_slopes.h |  1 +
 2 files changed, 41 insertions(+)

diff --git a/src/p_slopes.c b/src/p_slopes.c
index f52158a34..885987597 100644
--- a/src/p_slopes.c
+++ b/src/p_slopes.c
@@ -131,6 +131,36 @@ void P_ReconfigureViaVertexes (pslope_t *slope, const vector3_t v1, const vector
 	}
 }
 
+/// Setup slope via constants.
+static void ReconfigureViaConstants (pslope_t *slope, const fixed_t a, const fixed_t b, const fixed_t c, const fixed_t d)
+{
+	fixed_t m;
+	vector3_t *normal = &slope->normal;
+
+	// Set origin.
+	FV3_Load(&slope->o, 0, 0, c ? -FixedDiv(d, c) : 0);
+
+	// Get slope's normal.
+	FV3_Load(normal, a, b, c);
+	FV3_Normalize(normal);
+
+	// Invert normal if it's facing down.
+	if (normal->z < 0)
+		FV3_Negate(normal);
+
+	// Get direction vector
+	m = FixedHypot(normal->x, normal->y);
+	slope->d.x = -FixedDiv(normal->x, m);
+	slope->d.y = -FixedDiv(normal->y, m);
+
+	// Z delta
+	slope->zdelta = FixedDiv(m, normal->z);
+
+	// Get angles
+	slope->xydirection = R_PointToAngle2(0, 0, slope->d.x, slope->d.y)+ANGLE_180;
+	slope->zangle = InvAngle(R_PointToAngle2(0, 0, FRACUNIT, slope->zdelta));
+}
+
 /// Recalculate dynamic slopes.
 void T_DynamicSlopeLine (dynplanethink_t* th)
 {
@@ -680,6 +710,16 @@ pslope_t *P_SlopeById(UINT16 id)
 	return ret;
 }
 
+/// Creates a new slope from equation constants.
+pslope_t *MakeViaEquationConstants(const fixed_t a, const fixed_t b, const fixed_t c, const fixed_t d)
+{
+	pslope_t* ret = Slope_Add(0);
+
+	ReconfigureViaConstants(ret, a, b, c, d);
+
+	return ret;
+}
+
 /// Initializes and reads the slopes from the map data.
 void P_SpawnSlopes(const boolean fromsave) {
 	size_t i;
diff --git a/src/p_slopes.h b/src/p_slopes.h
index c87208597..27f2ec27b 100644
--- a/src/p_slopes.h
+++ b/src/p_slopes.h
@@ -88,6 +88,7 @@ fixed_t P_GetWallTransferMomZ(mobj_t *mo, pslope_t *slope);
 void P_HandleSlopeLanding(mobj_t *thing, pslope_t *slope);
 void P_ButteredSlope(mobj_t *mo);
 
+pslope_t *MakeViaEquationConstants(const fixed_t a, const fixed_t b, const fixed_t c, const fixed_t d);
 
 /// Dynamic plane type enum for the thinker. Will have a different functionality depending on this.
 typedef enum {