Drop Blocks


In minecraft when you mine a block, it drops the block to pick up. These blocks have to respond to what blocks are around them: if you put a block ontop of them, they have to move out of the way. They also have to fall with gravity.


I thought about how to solve this and went about the easiest and simplest solution. Each update loop the pickup block checks if it's inside a block, it it is, find the closest free block around it. I only check a 3 x 3 x 3 square i.e. one block from the block they're on. If no free block is found, just try to move upward. In code it looks like this:


float3 findClosestFreePosition(GameState *gameState, float3 startP, float3 defaultDir) {
float3 result = defaultDir;
float closestDist = FLT_MAX;
float3 startP_block = convertRealWorldToBlockCoords(startP);
bool found = false;

for(int z = -1; z <= 1; z++) {
for(int y = -1; y <= 1; y++) {
for(int x = -1; x <= 1; x++) {
if(x == 0 && y == 0 && z == 0) {
//NOTE: Don't test the block we're in
continue;
} else {

float3 offset = make_float3(x, y, z);

float3 blockP = plus_float3(offset, startP_block);

BlockChunkPartner blockPtr = blockExists(gameState, blockP.x, blockP.y, blockP.z, BLOCK_EXISTS_COLLISION);
if(!blockPtr.block) {
float3 dirVector = minus_float3(blockP, startP);
float d = float3_magnitude_sqr(dirVector);

if(d < closestDist) {
result = dirVector;
closestDist = d;
found = true;
}
}
}
}
}
}

return result;
}

Entity Update



Now that we have 'findClosestFreePosition' we can use it in the pickup block update function.


void updatePickupBlock() {
float3 accelForFrame = make_float3(0, 0, 0);

//NOTE: Convert the floating point position to which block it is inside
float3 worldP = convertRealWorldToBlockCoords(e->T.pos);

if(blockExistsReadOnly(gameState, worldP.x, worldP.y, worldP.z, BLOCK_EXISTS_COLLISION)) {
//NOTE: Pickup block is inside another block so moveout of the way
float3 moveDir = findClosestFreePosition(gameState, e->T.pos, make_float3(0, 1, 0), gameState->searchOffsets, arrayCount(gameState->searchOffsets), arrayCount(gameState->searchOffsets));
moveDir = normalize_float3(moveDir);
e->dP = make_float3(0, 0, 0);
accelForFrame = plus_float3(accelForFrame, scale_float3(100.0f, moveDir));

//NOTE: DEBUG code to place a red block if we are colliding. This is a helpful debug aid
pushAlphaCube(gameState->renderer, worldP, BLOCK_CLOUD, make_float4(1, 0, 0, 1.0f));
} else if(!blockExistsReadOnly(gameState, worldP.x, worldP.y -1 , worldP.z, BLOCK_EXISTS_COLLISION)) {
//NOTE: check if should apply gravity
accelForFrame.y = -10;
}

//NOTE: Integrate acceleration
e->dP = plus_float3(e->dP, scale_float3(gameState->dt, accelForFrame)); //NOTE: Already * by dt
//NOTE: Apply drag
e->dP = scale_float3(0.95f, e->dP);
//NOTE: Integrate velocity
e->T.pos = plus_float3(e->T.pos, scale_float3(gameState->dt, e->dP));
}


You can see the codebase here 👆