[Fix] Change the default semantic to a different slot which does not map to tangents

[mvaligursky]

Fixes #7824

use slot 11 (SEMANTIC_TEXCOORD6) instead of slot 13 (SEMANTIC_TANGENT), which is less likely to be used.

[MAG-AdrianMeredith]

Thanks Martin! (this came up today again, been playing with rendering the amazon lumberyard bistro)

[LeXXik]

If we use some of the slots for instancing, is there a way to tell which are used by the engine and which are free?

[mvaligursky]

If we use some of the slots for instancing, is there a way to tell which are used by the engine and which are free?

These are the default attributes engine uses for standard material (not all of them all the time, depends on material / mesh properties):

engine/src/scene/shader-lib/programs/lit-shader.js

Lines 28 to 36 in 2cc809e

	const builtinAttributes = {
	vertex_normal: SEMANTIC_NORMAL,
	vertex_tangent: SEMANTIC_TANGENT,
	vertex_texCoord0: SEMANTIC_TEXCOORD0,
	vertex_texCoord1: SEMANTIC_TEXCOORD1,
	vertex_color: SEMANTIC_COLOR,
	vertex_boneWeights: SEMANTIC_BLENDWEIGHT,
	vertex_boneIndices: SEMANTIC_BLENDINDICES
	};

and you can see the fixed mapping of semantic names to slots here:

engine/src/platform/graphics/constants.js

Lines 2148 to 2178 in 2cc809e

	semanticToLocation[SEMANTIC_POSITION] = 0;
	semanticToLocation[SEMANTIC_NORMAL] = 1;
	semanticToLocation[SEMANTIC_BLENDWEIGHT] = 2;
	semanticToLocation[SEMANTIC_BLENDINDICES] = 3;
	semanticToLocation[SEMANTIC_COLOR] = 4;
	semanticToLocation[SEMANTIC_TEXCOORD0] = 5;
	semanticToLocation[SEMANTIC_TEXCOORD1] = 6;
	semanticToLocation[SEMANTIC_TEXCOORD2] = 7;
	semanticToLocation[SEMANTIC_TEXCOORD3] = 8;
	semanticToLocation[SEMANTIC_TEXCOORD4] = 9;
	semanticToLocation[SEMANTIC_TEXCOORD5] = 10;
	semanticToLocation[SEMANTIC_TEXCOORD6] = 11;
	semanticToLocation[SEMANTIC_TEXCOORD7] = 12;
	semanticToLocation[SEMANTIC_TANGENT] = 13;
	semanticToLocation[SEMANTIC_ATTR0] = 0;
	semanticToLocation[SEMANTIC_ATTR1] = 1;
	semanticToLocation[SEMANTIC_ATTR2] = 2;
	semanticToLocation[SEMANTIC_ATTR3] = 3;
	semanticToLocation[SEMANTIC_ATTR4] = 4;
	semanticToLocation[SEMANTIC_ATTR5] = 5;
	semanticToLocation[SEMANTIC_ATTR6] = 6;
	semanticToLocation[SEMANTIC_ATTR7] = 7;
	semanticToLocation[SEMANTIC_ATTR8] = 8;
	semanticToLocation[SEMANTIC_ATTR9] = 9;
	semanticToLocation[SEMANTIC_ATTR10] = 10;
	semanticToLocation[SEMANTIC_ATTR11] = 11;
	semanticToLocation[SEMANTIC_ATTR12] = 12;
	semanticToLocation[SEMANTIC_ATTR13] = 13;
	semanticToLocation[SEMANTIC_ATTR14] = 14;
	semanticToLocation[SEMANTIC_ATTR15] = 15;

You could enable tracing for shader creation as well, and each created shader attributes it uses here:

engine/src/platform/graphics/shader.js

Line 51 in 2cc809e

attributes = new Map();

[LeXXik]

Great info, thanks!