We describe, here, the already converted productions between HLSL and GLSL.

Direct Token Mapping

HLSL	GLSL		HLSL	GLSL
#elseif	#elif		float2x2	mat2x2
float2	vec2		float2x3	mat2x3
float3	vec3		float2x4	mat2x4
float4	vec4		float3x2	mat3x2
bool2	bvec2		float3x3	mat3x3
bool3	bvec3		float3x4	mat3x4
bool4	bvec4		float4x2	mat4x2
int2	ivec2		float4x3	mat4x3
int3	ivec3		float4x4	mat4x4
int4	ivec4		tex2D	texture2D
half2	ivec2
half3	ivec3
half4	ivec4

Others Mappings

• #include: The pre-processing tag #include imports another file into the line where the tag is declared. Since GLSL does not have this feature, we need to import and parse that file.
• GLSL * operator between matrices, is the standard linear algebra matrix multiplication, while in HLSL is a component wise multiplication.
• Looks like HLSL cross params are backwards to what you had expect cross(T,N) equates to NxT, not TxN.
• GLSL doesn't support varying and uniform variables declared inside the parameters of a main function. They must be outside, like global vars.
• GLSL doesn't support two or more main functions in a file.
• Every GLSL file must have a main function with no arguments.
• GLSL does not support an 'f' after a float number (e.g. 1.0f).

Column Major or Row Major?

HLSL and GLSL matrices are both column major, but elements are accessed in this way:

HLSL

float4x4 = // [row][column]
 [0][0], [0][1], [0][2], [0][3]
 [1][0], [1][1], [1][2], [1][3]
 [2][0], [2][1], [2][2], [2][3]
 [3][0], [3][1], [3][2], [3][3]

float2x2 (
    0, 0, // row 1
    2, 2  // row 2) 

int1x1    iMatrix;   // integer matrix with 1 row,  1 column
int4x1    iMatrix;   // integer matrix with 4 rows, 1 column
int1x4    iMatrix;   // integer matrix with 1 row, 4 columns
double3x3 dMatrix;   // double matrix with 3 rows, 3 columns

matrix[0] returns the first row.

GLSL

float4x4 = // [column][row]
 [0][0], [0][1], [0][2], [0][3]
 [1][0], [1][1], [1][2], [1][3]
 [2][0], [2][1], [2][2], [2][3]
 [3][0], [3][1], [3][2], [3][3]

 mat2(float, float,  // first column
     float, float); // second column  

GLSL matrix[0] is the first column.

Semantic Params

There are no Semantic Params in GLSL. The variables that have semantical behavior must be replaced by declared variables. For example:

float4 oColor : Color

must be changed to

gl_FragColor

Intrinsic Functions that are not supported by GLSL

asuint	round
clip	saturate
cosh	sincos
D3DCOLORtoUBYTE4	sinh
determinant	tanh
frexp	tex1Dbias
GetRenderTargetSampleCount	tex1Dgrad
GetRenderTargetSamplePosition	tex2Dbias
isfinite	tex2Dgrad
isinf	tex3Dbias
isnan	tex3Dgrad
ldexp	texCUBEbias
lerp	texCUBEgrad
lit	transpose
log10	trunc
modf

HLSL Attributes Reference (Xbox 360)

This attributes are for shaders developed for Xbox360, thus, GLSL does not support them.

branch	maxtempreg
call	noExpressionOptimizations
flatten	predicateBlock
ifAll	reduceTempRegUsage
ifAny	removeUnusedInputs
isolate	sampreg
loop	unroll
maxexports	unused
maxInstructionCount