Move comments to docs, sign extend stuff for Android (#539)

* Move documentation, sign extend spot dir

* Update gles.patch

* Fix compilation errors

* Update gles.patch

docs/3ds/lighting.md

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+## Info on the lighting implementation
+
+### Missing shadow attenuation
+Shadow attenuation samples a texture unit, and that likely needs render to texture for most games so that they can construct
+their shadow map. As such the colors are not multiplied by the shadow attenuation value, so there's no shadows.
+
+### Missing bump mapping
+Bump mapping also samples a texture unit, most likely doesn't need render to texture however may need better texture sampling
+implementation (such as GPUREG_TEXUNITi_BORDER_COLOR, GPUREG_TEXUNITi_BORDER_PARAM). Bump mapping would work for some things,
+namely the 3ds-examples bump mapping demo, but would break others such as Toad Treasure Tracker with a naive `texture` implementation.
+
+Also the CP configuration is missing, because it needs a tangent map implementation. It is currently marked with error_unimpl.
+
+### samplerEnabledBitfields
+Holds the enabled state of the lighting samples for various PICA configurations
+As explained in https://www.3dbrew.org/wiki/GPU/Internal_Registers#GPUREG_LIGHTING_CONFIG0
+
+```c
+const bool samplerEnabled[9 * 7] = bool[9 * 7](
+	// D0     D1     SP     FR     RB     RG     RR
+	true,  false, true,  false, false, false, true,  // Configuration 0: D0, SP, RR
+	false, false, true,  true,  false, false, true,  // Configuration 1: FR, SP, RR
+	true,  true,  false, false, false, false, true,  // Configuration 2: D0, D1, RR
+	true,  true,  false, true,  false, false, false, // Configuration 3: D0, D1, FR
+	true,  true,  true,  false, true,  true,  true,  // Configuration 4: All except for FR
+	true,  false, true,  true,  true,  true,  true,  // Configuration 5: All except for D1
+	true,  true,  true,  true,  false, false, true,  // Configuration 6: All except for RB and RG
+	false, false, false, false, false, false, false, // Configuration 7: Unused
+	true,  true,  true,  true,  true,  true,  true   // Configuration 8: All
+);
+```
+
+The above has been condensed to two uints for performance reasons.
+You can confirm they are the same by running the following:
+```c
+const uint samplerEnabledBitfields[2] = { 0x7170e645u, 0x7f013fefu };
+for (int i = 0; i < 9 * 7; i++) {
+	unsigned arrayIndex = (i >> 5);
+	bool b = (samplerEnabledBitfields[arrayIndex] & (1u << (i & 31))) != 0u;
+	if (samplerEnabled[i] == b) {
+		printf("%d: happy\n", i);
+	} else {
+		printf("%d: unhappy\n", i);
+	}
+}
+```
+
+### lightLutLookup
+lut_id is one of these values
+0 	D0
+1 	D1
+2 	SP
+3 	FR
+4 	RB
+5 	RG
+6 	RR 
+
+lut_index on the other hand represents the actual index of the LUT in the texture
+u_tex_lighting_lut has 24 LUTs and they are used like so:
+0 		D0
+1 		D1
+2 		is missing because SP uses LUTs 8-15
+3 		FR
+4 		RB
+5 		RG
+6 		RR
+8-15 	SP0-7
+16-23 	DA0-7, but this is not handled in this function as the lookup is a bit different
+
+The light environment configuration controls which LUTs are available for use
+If a LUT is not available in the selected configuration, its value will always read a constant 1.0 regardless of the enable state in GPUREG_LIGHTING_CONFIG1
+If RR is enabled but not RG or RB, the output of RR is used for the three components; Red, Green and Blue.
+
+### Distance attenuation
+Distance attenuation is computed differently from the other factors, for example
+it doesn't store its scale in GPUREG_LIGHTING_LUTINPUT_SCALE and it doesn't use 
+GPUREG_LIGHTING_LUTINPUT_SELECT. Instead, it uses the distance from the light to the
+fragment and the distance attenuation scale and bias to calculate where in the LUT to look up.
+See: https://www.3dbrew.org/wiki/GPU/Internal_Registers#GPUREG_LIGHTi_ATTENUATION_SCALE