64 lines
3.8 KiB
HTML
64 lines
3.8 KiB
HTML
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<HTML>
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<HEAD>
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<TITLE>Controlling obstacles</TITLE></HEAD>
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<BODY>
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<h1>Controlling obstacles</h1>
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There are five main ways an object's movement around the screen can be limited:<p>
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<ul>
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<li>Control lines on the priority screen
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<li>Blocks
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<li>Land/water
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<li>The horizon
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<li>Other objects
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</ul>
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<p>
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For any of these, no part of the object's baseline (the bottom row of pixels of the object) can be on a part of the screen the object is not allowed on.<p>
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<B>Control lines on the priority screen</B><p>
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<p>
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On the priority screen, the first four colours (0-3) have special meaning. Colour 0 (black) is an unconditional barrier. No object is ever allowed to be on parts of the screen with a pixel of this
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colour in the priority screen.
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<p>
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Colour 1 (dark blue) is a conditional barrier. Objects are not normally allowed to be on a conditional barrier, unless the <a href="ignore_blocks.html">ignore.blocks</a> command is used to allow them to do so.<p>
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Colour 2 (dark green) is a signal barrier. This can be used to test if ego is walking into a certain place. Whenever ego is touching a signal barrier, flag 3 is set.<p>
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Colour 3(dark cyan) signifies water. This is explained shortly.<p>
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<B>Blocks</B><p>
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<p>
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You can set up an invisible rectangular block on the screen using the <a href="block.html">block</a> command. The interpreter will not allow objects to cross the borders of the block (unless they are told to ignore
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blocks). You can remove the block using the <a href="unblock.html">unblock</a> command. Objects can be told to ignore blocks using the <a href="ignore_blocks.html">ignore.blocks</a> command and be told to observe blocks by using
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the <a href="observe_blocks.html">objserve.blocks</a> command.
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<p>
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<B>Land/water</B><p>
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<p>
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Parts of the priority screen which are colour 3 (dark cyan) are considered to be "water". If you look at the priority screen of rooms that have lakes or rivers in them, you will usually see this. Parts
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of the priority screen which are not colour 3 are considered to be "land". You do not have to use colour 3 to represent water - it could also represent some other surface such as ice, lava, sand, a
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slippery floor, or whatever you need for that particular room.
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<p>
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Objects can be allowed only on water, only on land or on both. This is set be the <a href="object_on_water.html">object.on.water</a>, <a href="object_on_land.html">object.on.land</a> and <a href="object_on_anything.html">object.on.anything</a>
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commands.
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<p>
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Whenever ego's baseline is completely on water, flag 0 is set.<p>
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<B>The horizon</B><p>
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<p>
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The horizon is an invisible horizontal line, usually near the top of the screen. Its position is set using the <a href="set_horizon.html">set.horizon</a> command.<p>
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Normally, objects can not go above the horizon. This can be changed using the <a href="ignore_horizon.html">ignore.horizon</a> and <a href="observe_horizon.html">observe.horizon</a> commands.<p>
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<B>Other objects</B><p>
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<p>
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Objects are normally blocked by other objects on screen - that is, the baselines of objects are not allowed to touch each other. This can be changed, however, with the <a href="ignore_objs.html">ignore.objs</a> and
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<a href="observe_objs.html">observe.objs</a> commands.
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<p>
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<B>See also</B><p>
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<a href="block.html">block</a><p>
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<a href="unblock.html">unblock</a><p>
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<a href="ignore_blocks.html">ignore.blocks</a><p>
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<a href="observe_blocks.html">objserve.blocks</a><p>
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<a href="object_on_water.html">object.on.water</a><p>
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<a href="object_on_land.html">object.on.land</a><p>
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<a href="object_on_anything.html">object.on.anything</a><p>
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<a href="set_horizon.html">set.horizon</a><p>
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<a href="ignore_horizon.html">ignore.horizon</a><p>
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<a href="observe_horizon.html">observe.horizon</a><p>
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<a href="ignore_objs.html">ignore.objs</a><p>
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<a href="observe_objs.html">observe.objs</a><p>
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<a href="objects.html">Objects</a><p>
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</BODY></HTML>
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