Snapping mouse to grid

grid.lua

@@ -30,7 +30,7 @@ function Grid:draw()
     for x = 1, self.size.x do
         for y = 1, self.size.y do
             local px, py = x * Config.cellSize, y * Config.cellSize
-            love.graphics.circle( "fill", px, py, Config.pointRadius )
+            love.graphics.circle( "fill", px - Config.cellSize / 2, py - Config.cellSize / 2, Config.pointRadius)
         end
     end
 end

gridpoint.lua

@@ -14,5 +14,5 @@ end
 
 -- Same as coords, but converted to global coords
 function GridPoint:globalCoords()
-    return self.x * Config.cellSize, self.y * Config.cellSize
+    return self.x * Config.cellSize - Config.cellSize / 2, self.y * Config.cellSize - Config.cellSize / 2
 end

line.lua

@@ -38,6 +38,10 @@ function Line:draw()
     love.graphics.circle( "fill", sx, sy, Config.linePointRadius )
     local ex, ey = self.endpoint:globalCoords()
     love.graphics.circle( "fill", ex, ey, Config.linePointRadius )
+    if #self.points == 1 then
+        love.graphics.setColor( Color.white )
+        return
+    end
     -- Draw line
     local points = {}
     for _, point in ipairs( self.points ) do

main.lua

@@ -12,21 +12,35 @@ function love.load()
         GridPoint:new( 3, 3 ),
         Color.red
     )
-    line:push( GridPoint:new( 1, 2 ) )
-    line:push( GridPoint:new( 1, 3 ) )
-    line:push( GridPoint:new( 2, 3 ) )
-    line:push( GridPoint:new( 2, 2 ) )
-    line:push( GridPoint:new( 2, 1 ) )
-    line:push( GridPoint:new( 3, 1 ) )
-    line:push( GridPoint:new( 3, 2 ) )
-    line:push( GridPoint:new( 3, 3 ) )
     gameGrid:push( line )
+    mouse = {
+        x = 0,
+        y = 0,
+        pressed = false,
+        lastPressed = false
+    }
 end
 
+-- TODO: move input interactions into module
 function love.update( dt )
-    
+    mouse.x, mouse.y = love.mouse.getPosition()
+    mouse.lastPressed = pressed
+    mouse.pressed = love.mouse.isDown( 1 )
 end
 
 function love.draw()
     gameGrid:draw()
+
+    if mouse.pressed then
+        local x, y = snapCoords( Point:new( mouse.x, mouse.y ) ):coords()
+        local text = string.format( "%d:%d global\n%d:%d local", mouse.x, mouse.y, x, y )
+        love.graphics.print( text, 64, 256 )
+    end
+end
+
+-- Returns local coords from global
+function snapCoords( point )
+    local x = math.ceil( point.x / Config.cellSize )
+    local y = math.ceil( point.y / Config.cellSize )
+    return GridPoint:new( x, y )
 end