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[[File:0t sprintjump graph.png|thumb|600x600px|Movement formulas applied to a 3b jump.]] |
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<translate><!--T:2--> paragraph 1</translate> |
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The player's movement can be accurately calculated with [https://en.wikipedia.org/wiki/Sequence sequences]. |
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The following formulas come from analyzing the game's [[SourceCode|source code]]. |
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<translate><!--T:3--> paragraph 2</translate> |
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Note that these formulas are '''not exact''', due to how [https://en.wikipedia.org/wiki/Floating-point_arithmetic floats] are computed. When used for calculations, only the first 4-6 decimals should be considered accurate. For a completely accurate simulation, you would need to replicate the source code. |
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<translate><!--T:4--> [[File:Collision box (player and block).png|left|thumb|image 1]]</translate> |
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In this article, we only consider standard movement, and ignore mechanics specific to certain blocks. |
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You will find further documentation of movement physics in these articles: |
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* [[Soulsand]] |
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* [[Ladders and Vines|Ladders and Vines]] |
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* [[Slime Block|Slime Blocks]] |
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* [[Cobweb|Cobwebs]] |
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'''Note:''' Minecraft's coordinate system is oriented differently: 0° points towards "positive Z", and 90° points towards "negative X". We choose to work in the standard coordinate system to make calculations more intuitive. If need be, we can simply invert the X axis to match Minecraft's coordinate system. |
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<translate><!--T:5--> paragraph 3</translate> |
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<br /> |
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== Vertical Movement == |
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===Jump Formula=== |
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*<math>V\displaystyle _{Y,1} = 0.42</math> |
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* <math>V\displaystyle _{Y,t} = \left (V_{Y,t-1} - \underset{gravity}{0.08} \right ) \times \underset{drag}{0.98}</math> |
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:If <math display="inline"> \left | V\displaystyle _{Y,t} \right | < 0.005 </math>, <math display="inline">V\displaystyle _{Y,t}</math> is set to 0 instead (the player's height doesn't change for that tick) |
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:In 1.9+, it's compared to 0.003 instead. |
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'''Notes''' |
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*<math display="inline"> V\displaystyle _{Y,0}</math> isn't assigned a value because it has no importance. By convention, the 0<sup>th</sup> tick corresponds to the player's initial velocity before jumping. |
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*<math display="inline"> V\displaystyle _{Y,1}</math> corresponds to the initial jump motion. It is increased by 0.1 per level of [[Status Effects|Jump Boost]] |
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*Terminal velocity is -3.92 m/t |
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*When the player collides vertically with a block, vertical momentum is cancelled and only the acceleration is left. |
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===Vertical Position=== |
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: To get the position on a given tick, you simply need to sum <math display="inline">V\displaystyle _{Y}</math> |
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:<math display="inline">Y(n) = \sum_{t=1}^{n} V_{Y,t}</math> |
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===Jump duration=== |
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:The '''duration''' of a jump is the number of ticks between jumping and landing. |
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:It also corresponds to the period of that jump's cycle when performed repeatedly. |
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:This notion is linked to the notion of [[Tiers]]. |
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:{| class="wikitable" |
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!Description |
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!Duration |
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|- |
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|Flat Jump |
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|12 t |
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|- |
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|3bc Jump |
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|11 t |
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|- |
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|<nowiki>+0.5 Jump</nowiki> |
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|10 t |
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|- |
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| +1 Jump |
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|9 t |
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|- |
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|2.5bc Jump |
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|6 t |
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|- |
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|2bc Jump |
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|3 t |
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|- |
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|1.8125bc Jump |
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|2 t |
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|} |
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=== Source code === |
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'''from [[SourceCode:EntityLivingBase|EntityLivingBase]]''' |
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: <syntaxhighlight lang="java"> |
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/* Code unrelated to vertical movement is cut out */ |
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protected float getJumpUpwardsMotion(){ |
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return 0.42F; |
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} |
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protected void jump() |
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{ |
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this.motionY = this.getJumpUpwardsMotion(); |
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if (this.isPotionActive(Potion.jump)) |
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{ |
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this.motionY += (this.getActivePotionEffect(Potion.jump).getAmplifier() + 1) * 0.1F; |
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} |
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this.isAirBorne = true; |
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} |
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public void moveEntityWithHeading(float strafe, float forward) |
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{ |
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... /* also moves the player horizontally */ |
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this.motionY -= 0.08; |
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this.motionY *= 0.98; |
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} |
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public void onLivingUpdate() |
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{ |
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if (this.jumpTicks > 0) |
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--this.jumpTicks; |
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if (Math.abs(this.motionY) < 0.005D) |
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this.motionY = 0.0D; |
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if (this.isJumping) |
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{ |
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... /* different if in water or lava */ |
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if (this.onGround && this.jumpTicks == 0) |
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{ |
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this.jump(); |
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this.jumpTicks = 10; //activate autojump cooldown (0.5s) |
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} |
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} |
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else |
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{ |
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this.jumpTicks = 0; //reset autojump cooldown |
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} |
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... |
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this.moveEntityWithHeading(this.moveStrafing, this.moveForward); |
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} |
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</syntaxhighlight> |
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== Horizontal Movement == |
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Horizontal Movement is a bit more complex than Vertical Movement, as it relies on many more factors: player actions, direction, and ground slipperiness. |
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On every tick, the game does these three steps: |
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# Acceleration is added to the player's velocity. |
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# The player is moved (new position = position + velocity). |
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# The player's velocity is reduced to simulate drag. |
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We'll start by introducing Multipliers in an effort to make formulas more readable. |
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=== Multipliers === |
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: '''Movement Multiplier''' (See [[45 Strafe|45° Strafe]]) |
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:: <math>M_{t} = \begin{Bmatrix}1.3 & \textrm{Sprinting} \\ 1.0 & \textrm{Walking}\\ 0.3 & \textrm{Sneaking}\\ 0.0 & \textrm{Stopping} \end{Bmatrix} \times \begin{Bmatrix}0.98 & \textrm{Default}\\ 1.0 & \textrm{45° Strafe} \\ 0.98 \sqrt{2} & \textrm{45° Sneak} \end{Bmatrix}</math> |
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: '''Effects Multiplier''' (See [[Status Effects]]) |
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:: <math>E_{t} = (\underset{Decreases \; by \; 15\% \; per \; level \; of \; Slowness}{\underset{Increases \; by \; 20\% \; per \; level \; of \; Speed}{\underbrace{\left ( 1 + 0.2\times Speed \right ) \: \times\: \left ( 1 - 0.15\times Slowness \right )}}} \geq 0</math> |
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: '''Slipperiness Multiplier''' (See [[Slipperiness]]) |
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:: <math>S_{t} = \begin{Bmatrix}0.6 & \textrm{Default}\\ 0.8 & \textrm{Slime}\\ 0.98& \textrm{Ice} \\ 1.0 & \textrm{Airborne} \end{Bmatrix}</math> |
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: |
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<br /> |
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=== Linear Formulas === |
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: These simplified formulas only apply to linear movement (no change in direction). |
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:While this condition might seem very restrictive, these formulas are very useful to analyze conventional jumps and momentum |
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:We'll later expand on these formulas by including angles. |
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:<br />'''Definition''': |
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:* <math>V_{H,0}</math> is the player's initial speed (default = 0). |
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:* <math display="inline">V_{H,t}</math> is the player's speed on tick <math display="inline">t</math>. |
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: '''Ground Speed''': |
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::<math>V_{H,t} = \underset{Momentum}{\underbrace{\underset{ }{V_{H,t-1} \times S_{t-1} \times 0.91 }}} \: + \: \underset{Acceleration}{\underbrace{0.1 \times M_{t} \times E_{t} \times \left (\frac{0.6}{S_{t}} \right )^{3}}} </math> |
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: '''Jump Speed''': |
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::<math>V_{H,t} = \underset{Momentum}{\underbrace{\underset{ }{V_{H,t-1} \times S_{t-1} \times 0.91 }}} \: + \: \underset{Acceleration}{\underbrace{0.1 \times M_{t} \times E_{t} \times \left (\frac{0.6}{S_{t}} \right )^{3}}} + \underset{Sprintjump \; Boost}{\underbrace{\begin{Bmatrix}0.2 & \textrm{Sprinting}\\ 0.0 & \textrm{Else}\end{Bmatrix} }}</math> |
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: '''Air Speed''': |
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::<math>V_{H,t} = \underset{Momentum}{\underbrace{\underset{ }{V_{H,t-1} \times S_{t-1} \times 0.91 }}} \: + \: \underset{Acceleration}{\underbrace{\underset{ }{0.02 \times M_{t}}}} </math> |
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=== Complete Formulas === |
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: Let's introduce two more variables: |
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:*<math display="inline"> D_{t} </math> , The player's Direction in degrees (defined by their inputs and rotation) |
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:* <math display="inline"> F_{t} </math> , The player's Facing in degrees (defined by their rotation only) |
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In reality, angles aren't as simple as that, as there are a limited number of significant angles (see [[Facing and Angles]]). |
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For the purpose of simplicity, we'll ignore this fact. |
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: '''Definition''': |
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:* <math display="inline">V_{X,0}</math> and <math display="inline">V_{Z,0}</math> correspond to the player's initial velocity. |
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:* <math display="inline">V_{X,t}</math> and <math display="inline">V_{Z,t}</math> correspond to the player's velocity on tick <math display="inline">t</math> <br /> '''Ground Velocity''': |
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::<math>V\displaystyle _{X,t} = \underset{ }{V\displaystyle _{X,t-1} \times S_{t-1} \times 0.91 } \: + \: 0.1 \times M_{t} \times E_{t} \times \left (\frac{0.6}{S_{t}} \right )^{3} \times \sin (D_{t}) </math> |
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::<math>V\displaystyle _{Z,t} = \underset{Momentum}{\underbrace{\underset{ }{V\displaystyle _{Z,t-1} \times S_{t-1} \times 0.91 }}} \: + \: \underset{Acceleration}{\underbrace{0.1 \times M_{t} \times E_{t} \times \left (\frac{0.6}{S_{t}} \right )^{3}}} \times \cos (D_{t}) </math> |
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: '''Jump Velocity''': |
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::<math>V\displaystyle _{X,t} = \underset{ }{V\displaystyle _{X,t-1} \times S_{t-1} \times 0.91 } \: + \: 0.1 \times M_{t} \times E_{t} \times \left (\frac{0.6}{S_{t}} \right )^{3} \times \sin (D_{t}) + \begin{Bmatrix} 0.2 & \textrm{Sprinting}\\ 0.0 & \textrm{Else}\end{Bmatrix} \times \sin (F_{t}) </math> |
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::<math>V\displaystyle _{Z,t} = \underset{Momentum}{\underbrace{\underset{ }{V\displaystyle _{Z,t-1} \times S_{t-1} \times 0.91 }}} \: + \: \underset{Acceleration}{\underbrace{0.1 \times M_{t} \times E_{t} \times \left (\frac{0.6}{S_{t}} \right )^{3}}} \times \cos (D_{t}) + \underset{Sprintjump \; Boost }{\underbrace{\begin{Bmatrix} 0.2 & \textrm{Sprinting}\\ 0.0 & \textrm{Else}\end{Bmatrix} \times \cos (F_{t})}} </math> |
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: '''Air Velocity''': |
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::<math>V\displaystyle _{X,t} = \underset{ }{V\displaystyle _{X,t-1} \times S_{t-1} \times 0.91 } \: + \: 0.02 \times M_{t} \times \sin (D_{t}) </math> |
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::<math>V\displaystyle _{Z,t} = \underset{Momentum}{\underbrace{\underset{ }{V\displaystyle _{Z,t-1} \times S_{t-1} \times 0.91 }}} \: + \: \underset{Acceleration}{\underbrace{\underset{}{0.02 \times M_{t}}}} \times \cos (D_{t}) </math> |
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=== Stopping Conditions === |
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: Horizontal speed is set to 0 if the player hits a wall, or if the speed is considered to be negligible. |
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: '''Wall Collision''': |
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:: If the player hits a X-facing wall, then <math display="inline">V\displaystyle _{X,t}</math> is set to 0 and the player is placed against the wall. |
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:: If the player hits a Z-facing wall, then <math display="inline">V\displaystyle _{Z,t}</math> is set to 0 and the player is placed against the wall. |
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: '''Negligible Speed Threshold''': |
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:: If <math display="inline"> \left | V\displaystyle _{X,t} \times S_{t} \times 0.91 \right | < 0.005 </math> , momentum is cancelled and only the acceleration is left. |
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:: If <math display="inline"> \left | V\displaystyle _{Z,t} \times S_{t} \times 0.91 \right | < 0.005 </math> , momentum is cancelled and only the acceleration is left. |
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:: In 1.9+, they are compared to 0.003 instead. |
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=== Source Code === |
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[...] |
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<br /> |
Latest revision as of 04:37, 19 August 2021
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