ref: render code moved out of engine, doesn't compile, first API prototype

engine/common/mathlib.c

@@ -762,3 +762,50 @@ void QuaternionSlerp( const vec4_t p, const vec4_t q, float t, vec4_t qt )
 
 	QuaternionSlerpNoAlign( p, q2, t, qt );
 }
+
+/*
+====================
+V_CalcFov
+====================
+*/
+float V_CalcFov( float *fov_x, float width, float height )
+{
+	float	x, half_fov_y;
+
+	if( *fov_x < 1.0f || *fov_x > 179.0f )
+		*fov_x = 90.0f; // default value
+
+	x = width / tan( DEG2RAD( *fov_x ) * 0.5f );
+	half_fov_y = atan( height / x );
+
+	return RAD2DEG( half_fov_y ) * 2;
+}
+
+/*
+====================
+V_AdjustFov
+====================
+*/
+void V_AdjustFov( float *fov_x, float *fov_y, float width, float height, qboolean lock_x )
+{
+	float x, y;
+
+	if( width * 3 == 4 * height || width * 4 == height * 5 )
+	{
+		// 4:3 or 5:4 ratio
+		return;
+	}
+
+	if( lock_x )
+	{
+		*fov_y = 2 * atan((width * 3) / (height * 4) * tan( *fov_y * M_PI / 360.0 * 0.5 )) * 360 / M_PI;
+		return;
+	}
+
+	y = V_CalcFov( fov_x, 640, 480 );
+	x = *fov_x;
+
+	*fov_x = V_CalcFov( &y, height, width );
+	if( *fov_x < x ) *fov_x = x;
+	else *fov_y = y;
+}