Checklist

These mistakes were all found in real presets. For each one you get what goes wrong and how to avoid it. Avoid them and your presets will load and look the same in MilkDrop 2, in projectM players and in ProjectM TV.

The file

Do	Why	Real example
Put MILKDROP_PRESET_VERSION=201 and PSVERSION_WARP / PSVERSION_COMP first when you use shaders	Without them, shader code is ignored	1,506 bundled presets have no version line
Number code lines 1, 2, 3 … without gaps	Reading stops at the first missing number	—
Keep each name and number on one line	MilkDrop glues lines together; other engines don't	161.milk splits is_beat across two lines
Write key=value with no space before =	zoom =1 silently keeps the default	—
Write booleans as 0 and 1	-1 is true in MilkDrop, false in projectM	—
Always write wave_r, wave_g, wave_b, wave_x, wave_y	MilkDrop fills missing ones with 0, projectM with 1/1/1/0.5/0.5	—
Set PSVERSION_COMP=0 if you don't write a composite shader	projectM's empty-composite fallback skips gamma	—
Keep files under 1 MiB	Larger files fail to load in projectM	—

Equations

Do	Why	Real example
End every statement with ;, avoid ;), use // comments	Legacy forms only work in MilkDrop and ProjectM TV	index=index+1;);
Write 0, never a lone .	projectM's evaluator rejects .	y=if(c,.-.4,y);
Use int(rand(n)) for an integer	rand(n) returns a fraction	—
Guard divisions, pow, log, asin	The engines disagree on division by zero and domain errors	—
Copy values into q1–q32 every frame you need them	q resets to its post-init value each frame	—
Set motion variables every frame you change them	Built-ins reset to the file value each frame	—
Don't pass data to the next preset through reg/gmegabuf	They are per preset in projectM	—
Keep wave_mode within 0-7	projectM's modes 8-15 differ from MilkDrop's wrap-around	4 bundled presets use mode 8
Expect bass near 10 for a moment at a cold start	Audio history starts at zero	—
Remember warp defaults to 1	Set warp=0 for a still mesh	—

Shaders

Do	Why	Real example
Don't name variables sample, inf, nan	Reserved or ambiguous in GLSL	Flexi - madness portal.milk turned into a red disc
Initialize every global you read	Uninitialized globals read 0 on GLES, anything on D3D9	martin - organic light.milk (uv3)
Write one constructor per array element	Flat initializer lists can fail translation	ORB - Stahl - Glass Ocean
Copy an input before modifying it (float t = time;)	Writes to inputs need a per-invocation copy	$$$ Royal - Mashup (324)
Guard pow: pow(max(x,1e-6), y)	Negative or zero bases are undefined in GLSL	7 of the 12 unforecastable presets in the 100-preset audit
Use float literals (2.0) in float expressions	GLSL ES rejects some int/float mixes	EVET - Spiracology 2
Apply decay in your warp shader	MilkDrop ignores decay when a warp shader runs	—
Implement gamma/echo yourself in a custom composite	Classic display effects don't apply to it	—
Read blur with GetBlur1/2/3	Raw blur samplers return encoded values	—
Test multiplicative composites with dark and bright feedback	Channel products can crush to black	A bundled preset that looked "broken" was black by design

Textures

Do	Why	Real example
Choose filtering with fw_/fc_/pw_/pc_	sampler_state fields are ignored	ORB - Arctic Chill
Avoid image names like ab_stars.png	Any XY_ prefix is stripped: looked up as stars	—
Keep texture names unique ignoring case	Lookup is case-insensitive	—
Expect premultiplied alpha	Transparent pixels sample black	… rand tritex - inv play.milk
Design randNN for any image, or use a name prefix	Choices change on every load	192 bundled presets use random textures

Shapes, waves and blur

Do	Why	Real example
Keep important shapes at least two pixels wide at 1080p	Sub-pixel shapes may not light any pixel	amandio c - the green machine 2 … btbam covers sepultura.milk
Clamp colours to 0-1 in per-point code	Custom wave colours wrap around instead of clamping	—
Keep blur ranges at least 0.1 wide and nested	MilkDrop collapses narrow ranges; ProjectM TV repairs them, so the two look different	flexi - a julia fractal for hexcollie embossed (Jelly).milk
Use negative zoom only with zoomexp=1	Other combinations are undefined on GPUs	Hexcollie - This is where we begin stripped.milk

Before you share

1. Copy the presets into a checkout's core/src/main/assets/presets and run tools/check-presets.py (without --remove).
2. Watch the preset cold and after a minute of music, at 720p and at 4K.
3. Check the TV log for Preset code left out.
4. If you can, compare with MilkDrop 2 on Windows.