Add basic server-side tracing functionality

Restricted to L4D for now due to known ABI compatibility issues on other
branches. This should be easy to fix later when needed elsewhere.

Committer's note: I've counted myself as a joint author and added a
copyright notice to the .c file since this code is reasonably
modified from the code bill originally wrote last year.
but June of this year and , so I've gone ahead and
corrected his copyright notice too, with permission.

4 files changed, 163 insertions, 0 deletions

diff --git a/compile b/compile
index 17a1ba4..328c08b 100755
--- a/compile
+++ b/compile
@@ -81,6 +81,7 @@ src="\
 	os.c
 	portalcolours.c
 	sst.c
+	trace.c
 	xhair.c
 	x86.c"
 if [ "$dbg" = 1 ]; then src="$src \
diff --git a/compile.bat b/compile.bat
index ca632ed..a4a6a10 100644
--- a/compile.bat
+++ b/compile.bat
@@ -95,6 +95,7 @@ setlocal DisableDelayedExpansion
 :+ portalcolours.c

 :+ rinput.c

 :+ sst.c

+:+ trace.c

 :+ xhair.c

 :+ x86.c

 :: just tack these on, whatever (repeated condition because of expansion memes)

diff --git a/src/trace.c b/src/trace.c
new file mode 100644
index 0000000..0a301a7
--- /dev/null
+++ b/src/trace.c
@@ -0,0 +1,101 @@
+/*
+ * Copyright © 2023 Willian Henrique <wsimanbrazil@yahoo.com.br>
+ * Copyright © 2024 Michael Smith <mikesmiffy128@gmail.com>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED “AS IS” AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+ * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+ * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+ * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include "engineapi.h"
+#include "errmsg.h"
+#include "feature.h"
+#include "gametype.h"
+#include "intdefs.h"
+#include "trace.h"
+
+FEATURE()
+
+struct ray {
+	// these have type VectorAligned in the engine, which occupies 16 bytes
+	struct vec3f _Alignas(16) start, delta, startoff, extents;
+	// align to 16 since "extents" is supposed to occupy 16 bytes.
+    // TODO(compat): this member isn't in every engine branch
+	const float _Alignas(16) (*worldaxistransform)[3][4];
+	bool isray, isswept;
+};
+
+static void *srvtrace;
+
+DECL_VFUNC(void, TraceRay, 5, struct ray *, uint /*mask*/, void */*filter*/,
+		struct CGameTrace *)
+
+static inline bool nonzero(struct vec3f v) {
+	union { struct vec3f v; struct { unsigned int x, y, z; }; } u = {v};
+	return (u.x | u.y | u.z) << 1 != 0; // ignore sign bit
+}
+
+struct CGameTrace trace_line(struct vec3f start, struct vec3f end, uint mask,
+		void *filt) {
+	struct CGameTrace t;
+	struct vec3f delta = {end.x - start.x, end.y - start.y, end.z - start.z};
+	struct ray r = {
+		.isray = true,
+		.isswept = nonzero(delta),
+		.start = start,
+		.delta = delta
+	};
+	TraceRay(srvtrace, &r, mask, filt, &t);
+	return t;
+}
+
+struct CGameTrace trace_hull(struct vec3f start, struct vec3f end,
+		struct vec3f mins, struct vec3f maxs, uint mask, void *filt) {
+	struct CGameTrace t;
+	struct vec3f delta = {end.x - start.x, end.y - start.y, end.z - start.z};
+	struct vec3f extents = {
+		(maxs.x - mins.x) * 0.5f,
+		(maxs.y - mins.y) * 0.5f,
+		(maxs.z - mins.z) * 0.5f
+	};
+	struct ray r = {
+		// NOTE: could maybe hardcode this to false, but we copy engine logic
+		// just on the off chance we're tracing some insanely thin hull
+		.isray = (extents.x * extents.x + r.extents.y * r.extents.y +
+				extents.z * extents.z) < 1e-6,
+		.isswept = nonzero(delta),
+		.start = start,
+		.delta = delta,
+		.extents = extents,
+		.startoff = {
+			(mins.x + maxs.x) * -0.5f,
+			(mins.y + maxs.y) * -0.5f,
+			(mins.z + maxs.z) * -0.5f
+		}
+	};
+	TraceRay(srvtrace, &r, mask, filt, &t);
+	return t;
+}
+
+PREINIT {
+    // TODO(compat): restricting this to tested branches for now
+    return GAMETYPE_MATCHES(L4D);
+}
+
+INIT {
+    if (!(srvtrace = factory_engine("EngineTraceServer003", 0))) {
+		errmsg_errorx("couldn't get server-side tracing interface");
+		return false;
+	}
+    return true;
+}
+
+// vi: sw=4 ts=4 noet tw=80 cc=80
diff --git a/src/trace.h b/src/trace.h
new file mode 100644
index 0000000..82d2dac
--- /dev/null
+++ b/src/trace.h
@@ -0,0 +1,60 @@
+/*
+ * Copyright © 2023 Willian Henrique <wsimanbrazil@yahoo.com.br>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED “AS IS” AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+ * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+ * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+ * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#ifndef INC_TRACE_H
+#define INC_TRACE_H
+
+#include "intdefs.h"
+#include "engineapi.h"
+
+struct CBaseTrace {
+	struct vec3f startpos, endpos;
+	struct {
+		struct vec3f normal;
+		float dist;
+		u8 type, signbits;
+		//u8 pad[2];
+	} plane; // surface normal at impact
+	float frac;
+	int contents;
+	ushort dispflags;
+	bool allsolid, startsolid;
+};
+
+struct CGameTrace {
+	struct CBaseTrace base;
+	float fracleftsolid;
+	struct {
+		const char *name;
+		short surfprops;
+		ushort flags;
+	} surf;
+	int hitgroup;
+	short physbone;
+	ushort worldsurfidx; // not in every branch, but doesn't break ABI
+	void *ent; // CBaseEntity (C_BaseEntity in client.dll)
+	int hitbox;
+};
+
+struct CGameTrace trace_line(struct vec3f start, struct vec3f end, uint mask,
+		void *filt);
+
+struct CGameTrace trace_hull(struct vec3f start, struct vec3f end,
+		struct vec3f mins, struct vec3f maxs, uint mask, void *filt);
+
+#endif
+
+// vi: sw=4 ts=4 noet tw=80 cc=80