test: add `vision_test`

This test covers a few vision bugs:

1. VisibilityInStraightLineOfSight - test case checks the visibility
   of objects in a straight line of sight parallel to the X or Y
   coordinate lines:
   https://github.com/diasurgical/DevilutionX/pull/7901

2. NoVisibilityThroughAdjacentTiles - test case checks that nothing is
   visible through the diagonally adjacent tiles:
   https://github.com/diasurgical/DevilutionX/pull/7920

3. VisibleObjects - generic test, which makes sure some objects are
   visible, but some - are not.

Signed-off-by: Roman Penyaev <r.peniaev@gmail.com>

test/CMakeLists.txt

@@ -44,6 +44,7 @@ set(standalone_tests
   ini_test
   parse_int_test
   path_test
+  vision_test
   random_test
   rectangle_test
   static_vector_test
@@ -105,6 +106,7 @@ target_link_dependencies(format_int_test PRIVATE libdevilutionx_format_int langu
 target_link_dependencies(ini_test PRIVATE libdevilutionx_ini app_fatal_for_testing)
 target_link_dependencies(parse_int_test PRIVATE libdevilutionx_parse_int)
 target_link_dependencies(path_test PRIVATE libdevilutionx_pathfinding libdevilutionx_direction app_fatal_for_testing)
+target_link_dependencies(vision_test PRIVATE DevilutionX::SDL tl libdevilutionx_so app_fatal_for_testing)
 target_link_dependencies(path_benchmark PRIVATE libdevilutionx_pathfinding app_fatal_for_testing)
 target_link_dependencies(random_test PRIVATE libdevilutionx_random)
 target_link_dependencies(static_vector_test PRIVATE libdevilutionx_random app_fatal_for_testing)

test/vision_test.cpp

@@ -0,0 +1,182 @@
+#include <gtest/gtest.h>
+
+#include "lighting.h"
+
+namespace devilution {
+
+namespace {
+
+const uint8_t ENV_WIDTH = 25;
+const uint8_t ENV_HEIGHT = 25;
+
+// Real environment
+char env[ENV_WIDTH][ENV_HEIGHT];
+// Visible environment
+char vis[ENV_WIDTH][ENV_HEIGHT];
+// Observer position in the center of the environment
+const Point pos(ENV_WIDTH / 2, ENV_HEIGHT / 2);
+// Walls (box) around the observer with the specified radius
+const int box_radius = 4;
+// Objects around the observer: point, visible-to-observer flag
+const std::pair<Point, bool> objects[] = {
+	{ { 15, 12 }, true },
+	{ { 13, 15 }, true },
+	{ { 10, 11 }, true },
+	{ { 11, 13 }, true },
+	{ { 9, 15 }, false }, // Invisible to the observer, because of the {11,13}
+};
+
+// Build walls around with diagonally adjacent corners
+void buildWallsAround(char env[ENV_WIDTH][ENV_HEIGHT], Point p, int radius)
+{
+	for (int i = -radius + 1; i < radius; i++) {
+		env[p.x + radius][p.y + i] = '#';
+		env[p.x - radius][p.y + i] = '#';
+		env[p.x - i][p.y + radius] = '#';
+		env[p.x - i][p.y - radius] = '#';
+	}
+}
+
+void initEnvironment()
+{
+	memset(env, ' ', sizeof(env));
+	memset(vis, ' ', sizeof(vis));
+
+	// Build walls around with diagonally adjacent corners
+	buildWallsAround(env, pos, box_radius);
+
+	// Place objects
+	for (auto &o : objects) {
+		env[o.first.x][o.first.y] = '#';
+	}
+
+	// Place observer
+	env[pos.x][pos.y] = 'x';
+}
+
+void doVision()
+{
+	initEnvironment();
+
+	auto markVisibleFn = [](Point p) {
+		if (env[p.x][p.y] == ' ')
+			// Mark as hit by the ray
+			vis[p.x][p.y] = '.';
+		else
+			// Copy visible object
+			vis[p.x][p.y] = env[p.x][p.y];
+	};
+	auto markTransparentFn = [](Point p) {};
+	auto passesLightFn = [](Point p) {
+		return env[p.x][p.y] != '#';
+	};
+	auto inBoundsFn = [](Point p) { return true; };
+
+	DoVision(pos, 15, markVisibleFn, markTransparentFn, passesLightFn, inBoundsFn);
+}
+
+[[maybe_unused]]
+void dumpVisibleEnv()
+{
+	char buf[4096];
+	int sz = 0;
+	for (int i = 0; i < ENV_HEIGHT; i++) {
+		for (int j = 0; j < ENV_WIDTH; j++) {
+			sz += snprintf(buf + sz, sizeof(buf) - sz, "%c ", vis[i][j]);
+		}
+		sz += snprintf(buf + sz, sizeof(buf) - sz, "\n");
+	}
+	write(2, buf, sz);
+}
+
+// This test case checks the visibility of surrounding objects
+TEST(VisionTest, VisibleObjects)
+{
+	doVision();
+
+	for (auto &o : objects) {
+		if (o.second)
+			// Visible object
+			EXPECT_EQ(vis[o.first.x][o.first.y], '#') << "Expext visible wall or object";
+		else
+			// Invisible object
+			EXPECT_EQ(vis[o.first.x][o.first.y], ' ') << "Expect invisible tile";
+	}
+}
+
+// This test case checks the visibility of objects in a straight line
+// of sight parallel to the X or Y coordinate lines:
+// https://github.com/diasurgical/DevilutionX/pull/7901
+TEST(VisionTest, VisibilityInStraightLineOfSight)
+{
+	doVision();
+
+	Displacement displacements[] = { { 0, 1 }, { 1, 0 }, { 0, -1 }, { -1, 0 } };
+
+	for (auto &d : displacements) {
+		Point p = pos;
+		bool found = false;
+
+		// Move along the XY coordinate lines until a visible object is hit
+		while (p.x >= 0 && p.y >= 0 && p.x < ENV_WIDTH && p.y < ENV_HEIGHT) {
+			p += d;
+
+			if (vis[p.x][p.y] == '#') {
+				found = true;
+				break;
+			}
+		}
+		EXPECT_TRUE(found) << "Expect visible wall or object in a straight line of sight";
+	}
+}
+
+// This test case checks that nothing is visible through the
+// diagonally adjacent tiles:
+// https://github.com/diasurgical/DevilutionX/pull/7920
+TEST(VisionTest, NoVisibilityThroughAdjacentTiles)
+{
+	char mask[ENV_WIDTH][ENV_HEIGHT];
+
+	doVision();
+
+	memset(mask, ' ', sizeof(mask));
+	buildWallsAround(mask, pos, box_radius);
+
+	enum State {
+		BehindWall = 0,
+		HitWall,
+		OnWall,
+		InsideBox,
+	} state
+	    = BehindWall;
+
+	// Goes over each tile and compares the mask with the visible
+	// environment that is behind the wall
+	for (int i = 0; i < ENV_HEIGHT; i++) {
+		EXPECT_EQ(state, BehindWall);
+		for (int j = 0; j < ENV_WIDTH; j++) {
+			if (state == BehindWall) {
+				// Mask and environment are compared strictly behind
+				// the wall
+				EXPECT_EQ(mask[i][j], vis[i][j]) << "Expect no \"leaked\" light through adjacent tiles";
+			}
+
+			if (mask[i][j] == '#') {
+				if (state == BehindWall)
+					state = HitWall;
+				else if (state == HitWall)
+					state = OnWall;
+				else if (state == InsideBox)
+					state = BehindWall;
+			} else {
+				if (state == HitWall)
+					state = InsideBox;
+				else if (state == OnWall)
+					state = BehindWall;
+			}
+		}
+	}
+}
+
+} // namespace
+} // namespace devilution