Ah, I'm dumb. But perhaps my stupidity will save someone else the trouble...The trick I found is to turn up the "Snap Distance" in the "Tool Options" Preference panel. If you turn it up to 25, it snaps on all interactions, 15 is a reasonable medium, 8 is just too low for me.
Ah, that's a great find! I'd never have gone looking for it there. Thanks for posting the solution.
Thanks so much for creating this! It is enormously helpful to those of us who are very new with these editors to create something simple and cool. Altho I wish I had seen claud9999's comment at the end before I had started.
Until I get more experience at this, I'm going to have to go through this step by step a few times. I put together a mini-checklist from the original tutorial to make sure I don't forget anything as I work on new maps.
I use GameMastery flip-mats for my RPGs, which are 24 squares wide and 30 squares high, which explains some of the dimensions.
1. Create a canvas using "File > New". Assuming you use 50px squares, a 1000x1000-pixel image will create a 20x20 square grid. A 1200x1500-pixel image will create a 24x30 (flip-mat-size) grid. Setting the image to 160dpi should enable an output PDF of the (flip-mat) map to have a half-inch margin.
2. "View > Show Grid". This displays the default grid.
3. "Image > Configure Grid". Set the grid spacing to 50 pixels.
4. In the Layers Palette, choose "Patterns > Grid 50x50 blue". On your canvas, go to "Select > All" and then "Edit > Fill with Pattern". (Or "Filters > Render > Pattern > Grid" with Width 1, Spacing 50, Offset 0).
5. "Edit > Preferences". Go to "Tool Options" and raise the "Snap distance"; 25 will make the brush always snap to an intersection.
6. "View > Snap to Grid" should be checked.
7. In the Layers Palette, hit the "New Layer" button. Give the layer a name (such as Walls), and select Transparency as the Layer Fill Type. Make sure the new layer is selected.
8. Double-click the foreground color in the Toolbox Palette. Enter "18769d" in the "HTML notation" field.
9. In the Layers Palette, click on "Brushes" and select the "Circle (01) (3 x 3)" brush. A 9px brush creates a more visible internal wall.
Drawing and Coloring Walls
10. Draw some walls.
11. In the Toolbox Palette, choose the Fuzzy Select Tool, and make sure that "Sample merged" is off. On the canvas, click the area to be colored as impassable. Go to "Select > Grow..." and grow the selection by 2 pixels.
12. "Edit > Fill with FG Color". Repeat 11 and 12 to color in all the walls.
Placing Doors and Other Elements
13. "File > Open" and choose "door.png". "Select > All". "Edit > Copy". Close "door.png" without saving.
14. On the canvas, choose "Edit > Paste". In the Toolbox Palette, click the Rectangle Select Tool. Move the door and anchor it.