fix: fix geometry logic

src/apps/lua/lualilka_geometry.cpp

@@ -16,16 +16,19 @@ int lualilka_geometry_intersectLines(lua_State* L) {
     float dx = luaL_checknumber(L, 7);
     float dy = luaL_checknumber(L, 8);
 
-    // I have no idea what I'm doing - Copilot wrote this for me, lol
+    // Solve A + t * (B - A) = C + u * (D - C) using 2D cross products: segments intersect when t, u are in [0, 1]
+    float rx = bx - ax, ry = by - ay; // B - A
+    float sx = dx - cx, sy = dy - cy; // D - C
+    float qx = cx - ax, qy = cy - ay; // C - A
 
-    float denominator = (by - ay) * (dx - cx) - (bx - ax) * (dy - cy);
+    float denominator = rx * sy - ry * sx;
     if (denominator == 0) {
         lua_pushboolean(L, false);
         return 1;
     }
 
-    float t = ((cy - ay) * (dx - cx) - (cx - ax) * (dy - cy)) / denominator;
-    float u = -((ay - by) * (cx - ax) - (ax - bx) * (cy - ay)) / denominator;
+    float t = (qx * sy - qy * sx) / denominator;
+    float u = (qx * ry - qy * rx) / denominator;
 
     if (t >= 0 && t <= 1 && u >= 0 && u <= 1) {
         lua_pushboolean(L, true);

src/apps/lua/lualilka_imageTransform.cpp

@@ -67,7 +67,7 @@ static int lualilka_imageTransform_get_matrix(lua_State* L) {
     for (int i = 0; i < 2; ++i) {
         lua_newtable(L);
         for (int j = 0; j < 2; ++j) {
-            lua_pushinteger(L, (*userdata)->matrix[i][j]);
+            lua_pushnumber(L, (*userdata)->matrix[i][j]);
             lua_rawseti(L, -2, j + 1);
         }
         lua_rawseti(L, -2, i + 1);
@@ -77,26 +77,27 @@ static int lualilka_imageTransform_get_matrix(lua_State* L) {
 
 static int lualilka_imageTransform_set_matrix(lua_State* L) {
     lilka::Transform** userdata = TRANSFORM_PTR(luaL_checkudata(L, 1, IMAGE_TRANSFORM));
-    if (!lua_istable(L, 2)) {
-        return luaL_error(L, "Expected a table as the second argument");
-    }
+    luaL_checktype(L, 2, LUA_TTABLE);
 
+    // Validate the whole matrix first, so a bad argument leaves the transform untouched
+    float matrix[2][2];
     for (int i = 0; i < 2; ++i) {
-        lua_rawgeti(L, 2, i + 1);
+        if (lua_rawgeti(L, 2, i + 1) != LUA_TTABLE) {
+            return luaL_error(L, "Expected a 2x2 table, row %d is not a table", i + 1);
+        }
         for (int j = 0; j < 2; ++j) {
             lua_rawgeti(L, -1, j + 1);
-
-            if (!lua_isnumber(L, -1)) {
-                lua_pop(L, 2);
-                return luaL_error(L, "Element at (%d, %d) is not a number", i, j);
+            int isNumber = 0;
+            matrix[i][j] = lua_tonumberx(L, -1, &isNumber);
+            if (!isNumber) {
+                return luaL_error(L, "Element at (%d, %d) is not a number", i + 1, j + 1);
             }
-
-            (*userdata)->matrix[i][j] = lua_tonumber(L, -1);
             lua_pop(L, 1);
         }
-
         lua_pop(L, 1);
     }
+
+    memcpy((*userdata)->matrix, matrix, sizeof(matrix));
     return 0;
 }
 

src/apps/lua/luarunner.cpp

@@ -249,13 +249,27 @@ void AbstractLuaRunnerApp::luaTeardown() {
     lua_close(L);
 }
 
+void AbstractLuaRunnerApp::resetCanvasState() {
+    for (lilka::Canvas* c : {canvas, backCanvas}) {
+        if (!c) continue;
+        // Match defaults of a freshly constructed lilka::Canvas
+        c->setFont(FONT_10x20);
+        c->setTextBound(0, 0, c->width(), c->height());
+        c->setTextColor(lilka::colors::White);
+        c->setTextSize(1);
+        c->setTextWrap(true);
+        c->setCursor(0, 0);
+    }
+}
+
 int AbstractLuaRunnerApp::execute() {
     // Calls Lua code that's on top of the stack (previously loaded with luaL_loadfile or luaL_loadstring)
 
     int jmpCode = setjmp(stopjmp);
 
     if (jmpCode == 0) {
         // Run script
+        resetCanvasState();
         canvas->fillScreen(0);
         int retCode = lua_pcall(L, 0, LUA_MULTRET, 0);
         if (retCode) {

src/apps/lua/luarunner.h

@@ -28,6 +28,8 @@ class AbstractLuaRunnerApp : public App {
     void luaSetup(const char* dir);
     void luaTeardown();
     int execute();
+    // Restore default text state on both canvas buffers, so scripts don't inherit runner UI settings
+    void resetCanvasState();
     lua_State* L;
 };
 

src/apps/mjs/mjsgeometry.cpp

@@ -12,14 +12,19 @@ static void mjs_geometry_intersect_lines(struct mjs* mjs) {
     float dx = mjs_get_double(mjs, mjs_arg(mjs, 6));
     float dy = mjs_get_double(mjs, mjs_arg(mjs, 7));
 
-    float denominator = (by - ay) * (dx - cx) - (bx - ax) * (dy - cy);
+    // Solve A + t * (B - A) = C + u * (D - C) using 2D cross products: segments intersect when t, u are in [0, 1]
+    float rx = bx - ax, ry = by - ay; // B - A
+    float sx = dx - cx, sy = dy - cy; // D - C
+    float qx = cx - ax, qy = cy - ay; // C - A
+
+    float denominator = rx * sy - ry * sx;
     if (denominator == 0) {
         mjs_return(mjs, mjs_mk_boolean(mjs, 0));
         return;
     }
 
-    float t = ((cy - ay) * (dx - cx) - (cx - ax) * (dy - cy)) / denominator;
-    float u = -((ay - by) * (cx - ax) - (ax - bx) * (cy - ay)) / denominator;
+    float t = (qx * sy - qy * sx) / denominator;
+    float u = (qx * ry - qy * rx) / denominator;
 
     mjs_return(mjs, mjs_mk_boolean(mjs, t >= 0 && t <= 1 && u >= 0 && u <= 1));
 }