{"id":6059,"date":"2016-11-26T11:01:32","date_gmt":"2016-11-26T16:01:32","guid":{"rendered":"https:\/\/www.caskeys.com\/dc\/?p=6059"},"modified":"2017-01-15T15:23:56","modified_gmt":"2017-01-15T20:23:56","slug":"code-snip-collision-checking","status":"publish","type":"post","link":"https:\/\/www.caskeys.com\/dc\/code-snip-collision-checking\/","title":{"rendered":"Code Snip – Collision Checking"},"content":{"rendered":"

Notes from 2016-11-26 – Revamping OpenBOR collision detection.<\/p>\n

\"With<\/a>
With the possibility of several dozen or more entities on screen, collision detection must be precise with minimal resource intensity.<\/figcaption><\/figure>\n

Currently coordinates (s_hitbox) exist as static sub-structures in s_collision_attack<\/em> and s_collision_body<\/em>. See below…<\/p>\n

\r\ntypedef struct\r\n{\r\n\tint x;\r\n\tint y;\r\n\tint width;\r\n\tint height;\r\n\tint z1;\r\n\tint z2;\r\n} s_hitbox;\r\n\r\n\/\/ s_collision_attack\r\ntypedef struct\r\n{\r\n    int                 attack_drop;        \/\/ now be a knock-down factor, how many this attack will knock victim down\r\n    int                 attack_force;\r\n    int                 attack_type;        \/\/ Reaction animation, death, etc.\r\n    int                 blast;              \/\/ Attack box active on hit opponent's fall animation.\r\n    int                 blockflash;         \/\/ Custom bflash for each animation, model id\r\n    int                 blocksound;         \/\/ Custom sound for when an attack is blocked\r\n    s_hitbox            coords;\r\n    int                 counterattack;      \/\/ Treat other attack boxes as body box.\r\n    ...\r\n<\/pre>\n
This was done for simplicity, and with current logic wastes no memory as coordinates are always required for a collision box.<\/p>\n
However, the addition of multiple collision box support has exposed the need to break collision detection down into smaller functions. This in turn requires a lot of passing around the entire s_hitbox<\/em> structure. Given the rate this functionality is used (multiple collision evaluations on every entity on every animation frame @200 frames per second), efficiency is absolutely imperative. Replacing the static coords<\/em> declaration with a pointer and using dynamic allocation will add some code complexity initially, but in the long term should simplify breaking down collision logic and save substantial resources.<\/p>\n
The following are in progress logic functions, they will need reworking to accommodate new pointer.<\/p>\n
\r\n\/\/ Caskey, Damon V.\r\n\/\/ 2016-11-25\r\n\/\/\r\n\/\/ Get 2D size and position of collision box.\r\ns_coords_box_2D collision_final_coords_2D(entity *entity, s_hitbox coords)\r\n{\r\n    s_hitbox        temp;\r\n    s_coords_box_2D result;\r\n\r\n    temp.z1 = 0;\r\n\r\n    \/\/ If Z coords are reversed, let's correct them.\r\n    \/\/ Otherwise we use\r\n    if(coords.z2 &gt; coords.z1)\r\n    {\r\n        temp.z1 = coords.z1 + (coords.z2 - coords.z1) \/ 2;\r\n    }\r\n\r\n    \/\/ Get entity positions with Z offset\r\n    \/\/ included, and cast to integer.\r\n    temp.x    = (int)(entity-&gt;position.x);\r\n    temp.y    = (int)(temp.z1 - entity-&gt;position.y);\r\n\r\n    \/\/ Use temporary positions to get final dimensions\r\n    \/\/ for collision boxes.\r\n    if(entity-&gt;direction == DIRECTION_LEFT)\r\n    {\r\n        result.position.x   = temp.x - coords.width;\r\n        result.size.x       = temp.x - coords.x;\r\n    }\r\n    else\r\n    {\r\n        result.position.x   = temp.x + coords.x;\r\n        result.size.x       = temp.x + coords.width;\r\n    }\r\n    result.position.y   = temp.y + coords.y;\r\n    result.size.y       = temp.y + coords_owner.height;\r\n\r\n    return result;\r\n}\r\n\r\nbool collision_check_contact_2D(s_coords_box_2D owner, s_coords_box_2D target)\r\n{\r\n    \/\/ Compare the calculated boxes. If any one check\r\n    \/\/ fails, then the boxes are not in contact.\r\n    if(owner.position.x &gt; target.size.x)\r\n    {\r\n        return FALSE;\r\n    }\r\n    if(target.position.x &gt; target.size.x)\r\n    {\r\n        return FALSE;\r\n    }\r\n    if(owner.position.y &gt; target.size.y)\r\n    {\r\n        return FALSE;\r\n    }\r\n    if(target.position.y &gt; target.size.y)\r\n    {\r\n        return FALSE;\r\n    }\r\n}\r\n\r\nbool collision_check_contact_Z(entity *owner, s_hitbox coords_owner, s_hitbox coords_target)\r\n{\r\n    int Z_distance = 0;\r\n    int z1 = 0;\r\n    int z2 = 0;\r\n\r\n    if(coords_owner.z2 &gt; coords_owner.z1)\r\n    {\r\n        z1 += coords_owner.z1 + (coords_owner.z2 - coords_owner.z1) \/ 2;\r\n        zdist = (coords_owner.z2 - coords_owner.z1) \/ 2;\r\n    }\r\n    else if(coords_owner.z1)\r\n    {\r\n        zdist += coords_owner.z1;\r\n    }\r\n    else\r\n    {\r\n        zdist += attacker-&gt;modeldata.grabdistance \/ 3 + 1;    \/\/temporay fix for integer to float conversion\r\n    }\r\n\r\n    if(coords_target.z2 &gt; coords_target.z1)\r\n    {\r\n        z2 += coords_target.z1 + (coords_target.z2 - coords_target.z1) \/ 2;\r\n        zdist += (coords_target.z2 - coords_target.z1) \/ 2;\r\n    }\r\n    else if(coords_target.z1)\r\n    {\r\n        zdist += coords_target.z1;\r\n    }\r\n\r\n    zdist++; \/\/ pass &gt;= &lt;= check if(diff(z1, z2) &gt; zdist)\r\n    {\r\n        return FALSE;\r\n    }\r\n    \r\n    return TRUE; \r\n}\r\n\r\n\/\/ Caskey, Damon V.\r\n\/\/ 2016-11-25\r\n\/\/\r\n\/\/ Compare collision boxes and return\r\n\/\/ TRUE if they are in contact.\r\nbool checkhit_collision(entity *owner, entity *target, s_hitbox coords_owner, s_hitbox coords_target)\r\n{\r\n    s_coords_box_2D owner_final;\r\n    s_coords_box_2D target_final;\r\n\r\n    bool result;\r\n    \r\n    \/\/ First check Z contact.\r\n    result = collision_check_contact_Z(owner, coords_owner, coords_target);    \r\n\r\n    \/\/ If result is TRUE, then run\r\n    \/\/ 2D plane checks.\r\n    if(result)\r\n    {\r\n        \/\/ Get final collision box 2D plane sizes.\r\n        owner_final     = collision_final_coords_2D(owner, coords_owner);\r\n        target_final    = collision_final_coords_2D(target, coords_target);\r\n        \r\n        \/\/ Compare the 2D boxes and get result.\r\n        result = collision_check_contact_2D(owner_final, target_final);\r\n    }\r\n    \r\n    \/\/ return final result.\r\n    return result;\r\n}\r\n\r\n\/\/ Find center of attack area\r\ns_axis_f_2d collision_center()\r\n{\r\n\r\n    leftleast = attack_pos_x;\r\n\r\n    if(leftleast &lt; detect_pos_x) { leftleast = detect_pos_x; } rightleast = attack_size_x; if(rightleast &gt; detect_size_x)\r\n    {\r\n        rightleast = detect_size_x;\r\n    }\r\n\r\n    medx = (float)(leftleast + rightleast) \/ 2;\r\n}\r\n<\/pre>\n","protected":false},"excerpt":{"rendered":"
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