Re: Help with Pointers
- Posted by ghaberek (admin) 4 days ago
- 106 views
C example being ported to Eu [https://github.com/ColleagueRiley/RGFW/blob/main/examples/gears/gears.c]
//From gl.h WINGDIAPI void APIENTRY glLightiv(GLenum light,GLenum pname,const GLint *params);
OpenGL functions follow a predictable nomenclature:
Function type suffixes are typically defined in the following pattern:
FunctionName{1234}{b s i i64 f d ub us ui ui64}{v}
The first set of braces is an optional number from 1 to 4. This defines the number of parameters of those types that the function takes.
The second set of braces defines the types themselves, as defined by the table to the left.
If the optional v suffix is provided, this means the function takes a "vector": a pointer to an array of some number of values.
The function glLightiv takes a vector (a pointer to an array) of GLint values. Sometimes, however, the number of values in the array varies based on some parameter.
In the case of glLight, you have to consult the options for the pname parameter to determine how many values you actually need to provide in the params array.
The ten light parameters are as follows:
- GL_AMBIENT - four integer or floating-point values
- GL_DIFFUSE - four integer or floating-point values
- GL_SPECULAR - four integer or floating-point values
- GL_POSITION - four integer or floating-point values
- GL_SPOT_DIRECTION - three integer or floating-point values
- GL_SPOT_EXPONENT - a single integer or floating-point value
- GL_SPOT_CUTOFF - a single integer or floating-point value
- GL_CONSTANT_ATTENUATION - a single integer or floating-point value
- GL_LINEAR_ATTENUATION - a single integer or floating-point value
- GL_QUADRATIC_ATTENUATION - a single integer or floating-point value
I would say that technically all you have to do is feed it any number of integers and assume they line up.
public procedure glLightiv(integer light, integer pname, sequence params) atom pparams = allocate_data(sizeof(C_INT) * length(params)) poke4(pparams, params) c_proc(_glLightiv, {light,pname,pparams}) free(pparams) end procedure
Given the max seems to be four values, you could just "round up" by padding the remaining values first.
public procedure glLightiv(integer light, integer pname, sequence params) if length(params) < 4 then params &= repeat(0, 4-length(params)) end if atom pparams = allocate_data(sizeof(C_INT) * length(params)) poke4(pparams, params) c_proc(_glLightiv, {light,pname,pparams}) free(pparams) end procedure
But to be safe, you should check the length of params corresponds to the provided pname value.
public procedure glLightiv(integer light, integer pname, sequence params) integer required = 0 switch pname do case GL_AMBIENT, GL_DIFFUSE, GL_SPECULAR, GL_POSITION then required = 4 case GL_SPOT_DIRECTION then required = 3 case GL_SPOT_EXPONENT, GL_SPOT_CUTOFF, GL_CONSTANT_ATTENUATION, GL_LINEAR_ATTENUATION, GL_QUADRATIC_ATTENUATION then required = 1 end switch if required != length(params) then error:crash("expected %d params but received %d", {required,length(params)}) end if atom pparams = allocate_data(sizeof(C_INT) * length(params)) poke4(pparams, params) c_proc(_glLightiv, {light,pname,pparams}) free(pparams) end procedure
-Greg
