Found by looking at the decompiled Minecraft Classic source code in ClassiCube client.
Note: All variable names were made up in the process of deobfuscating the code.
Relevant variables starting values:
bool applyBreakAnim = false;
int breakAnimTicks = 7; //how many ticks it takes for the block break animation to complete. Never changes
int breakTimer = 0;
EVERY TICK:
Add 1 to breakTimer
If breakTimer is equal to breakAnimTicks, set applyBreakAnim to false and set breakTimer to 0.
EVERY TIME YOU CLICK TO START THE ANIMATION (checked on tick):
breakTimer = -1
applyBreakAnim = true;
EVERY FRAME:
if applyBreakAnim is true...
creates an elapsedTicks, which is the current breakTimer plus delta
creates lerp, which is elapsedTicks divided by breakAnimTicks
creates sinHalfCircle, which is sin(lerp * PI)
creates sqrtLerpPI, which is the square root(lerp) * PI.
Then, moves the block on...
X by -sin(sqrtLerpPI) * 0.4
Y by sin(sqrtLerpPI * 2) * 0.2
Z by -sinHalfCircle * 0.2
Note: Z should be forward/back in this case, if it isn't already in CS
end if.
Intermission: SET HELD BLOCK POSITION AT THIS POINT
if applyBreakAnim is true...
(There will be variable re-use from the first if statement in here.)
creates sinHalfCircleWeird, which is sin(lerp * lerp * PI)
rotates on Y axis by sin(sqrtLerpPI) * 80
rotates on X axis by -sinHalfCircleWeird * 20
end if.
If it's not your hand, scale down by 0.4
If it's your hand, set hand position here.
