digitalmars.D.learn - Passing dynamic arrays into C.
- Bernard Helyer (22/22) Apr 25 2010 I was having a problem interfacing with OpenGL from D, as demonstrated
- Daniel Murphy (17/38) Apr 25 2010 It should work if you treat the dynamic array like a pointer and a lengt...
- Bernard Helyer (4/59) Apr 25 2010 Ah, thank you!
- bearophile (9/13) Apr 25 2010 Are you sure that vertices.sizeof is right? It can be wrong. Maybe you w...
- Bernard Helyer (3/16) Apr 25 2010 Guilty on all charges. Confused the behaviour of static and dynamic
I was having a problem interfacing with OpenGL from D, as demonstrated
by this program, written once in D, and again in C:
http://gist.github.com/378273
Now the 'gist' of it is, doing things like this (D):
glBufferData(GL_ARRAY_BUFFER, vertices.sizeof,
vertices.ptr, GL_STATIC_DRAW);
glVertexPointer(2, GL_FLOAT, GLfloat.sizeof * 2, cast(void*)0);
With this data (D):
const GLfloat[] vertices = [-1.0f, -1.0f, 1.0f, -
1.0f, -1.0f, 1.0f, 1.0f, 1.0f];
and the same data in C:
const GLfloat vertices[] = {-1.0f, -1.0f, 1.0f,
-1.0f, -1.0f, 1.0f, 1.0f, 1.0f};
I was getting nothing but a blank screen. I'm sure you smart folks know
what comes next.
GLfloat[] vertices = {1.0f, 1.0f}; // vertices is a dynamic array.
GLfloat[2] vertices = {1.0f, 1.0f}; // vertices is a static array.
The second version enables the program to work as the C one does.
My question is, why doesn't passing the `GLfloat[] vertex ...`
declaration work? I've looked through the docs, and can't see anything
too obvious.
Thanks.
Apr 25 2010
It should work if you treat the dynamic array like a pointer and a length.
eg:
glBufferData(GL_ARRAY_BUFFER, (vertices[0]).sizeof * vertices.length,
vertices.ptr, GL_STATIC_DRAW);
It's probably because (type).sizeof gives the number of bytes to hold the
type.
For dynamic arrays, this is the size of the (length, pointer) pair and not
the array itself.
float.sizeof // gives 4
int.sizeof // gives 4
int[].sizeof // gives 8
int[3].sizeof // gives 12
class C { int[100] d; };
C.sizeof // gives the size of the reference, not the instance.
I haven't checked the sizes, but it generally follows something like that.
"Bernard Helyer" <b.helyer gmail.com> wrote in message
news:hr0veq$2269$1 digitalmars.com...
I was having a problem interfacing with OpenGL from D, as demonstrated by
this program, written once in D, and again in C:
http://gist.github.com/378273
Now the 'gist' of it is, doing things like this (D):
glBufferData(GL_ARRAY_BUFFER, vertices.sizeof,
vertices.ptr, GL_STATIC_DRAW);
glVertexPointer(2, GL_FLOAT, GLfloat.sizeof * 2, cast(void*)0);
With this data (D):
const GLfloat[] vertices = [-1.0f, -1.0f, 1.0f, -
1.0f, -1.0f, 1.0f, 1.0f, 1.0f];
and the same data in C:
const GLfloat vertices[] = {-1.0f, -1.0f, 1.0f,
-1.0f, -1.0f, 1.0f, 1.0f, 1.0f};
I was getting nothing but a blank screen. I'm sure you smart folks know
what comes next.
GLfloat[] vertices = {1.0f, 1.0f}; // vertices is a dynamic array.
GLfloat[2] vertices = {1.0f, 1.0f}; // vertices is a static array.
The second version enables the program to work as the C one does.
My question is, why doesn't passing the `GLfloat[] vertex ...` declaration
work? I've looked through the docs, and can't see anything too obvious.
Thanks.
Apr 25 2010
Bernard Helyer <b.helyer gmail.com>
Ah, thank you!
The problem was I read the way T[].sizeof behaves on static arrays,
thinking I was reading the section on dynamic array properties.
On 25/04/10 21:52, Daniel Murphy wrote:
It should work if you treat the dynamic array like a pointer and a length.
eg:
glBufferData(GL_ARRAY_BUFFER, (vertices[0]).sizeof * vertices.length,
vertices.ptr, GL_STATIC_DRAW);
It's probably because (type).sizeof gives the number of bytes to hold the
type.
For dynamic arrays, this is the size of the (length, pointer) pair and not
the array itself.
float.sizeof // gives 4
int.sizeof // gives 4
int[].sizeof // gives 8
int[3].sizeof // gives 12
class C { int[100] d; };
C.sizeof // gives the size of the reference, not the instance.
I haven't checked the sizes, but it generally follows something like that.
"Bernard Helyer"<b.helyer gmail.com> wrote in message
news:hr0veq$2269$1 digitalmars.com...
I was having a problem interfacing with OpenGL from D, as demonstrated by
this program, written once in D, and again in C:
http://gist.github.com/378273
Now the 'gist' of it is, doing things like this (D):
glBufferData(GL_ARRAY_BUFFER, vertices.sizeof,
vertices.ptr, GL_STATIC_DRAW);
glVertexPointer(2, GL_FLOAT, GLfloat.sizeof * 2, cast(void*)0);
With this data (D):
const GLfloat[] vertices = [-1.0f, -1.0f, 1.0f, -
1.0f, -1.0f, 1.0f, 1.0f, 1.0f];
and the same data in C:
const GLfloat vertices[] = {-1.0f, -1.0f, 1.0f,
-1.0f, -1.0f, 1.0f, 1.0f, 1.0f};
I was getting nothing but a blank screen. I'm sure you smart folks know
what comes next.
GLfloat[] vertices = {1.0f, 1.0f}; // vertices is a dynamic array.
GLfloat[2] vertices = {1.0f, 1.0f}; // vertices is a static array.
The second version enables the program to work as the C one does.
My question is, why doesn't passing the `GLfloat[] vertex ...` declaration
work? I've looked through the docs, and can't see anything too obvious.
Thanks.
Apr 25 2010
Bernard Helyer:
glBufferData(GL_ARRAY_BUFFER, vertices.sizeof,
vertices.ptr, GL_STATIC_DRAW);
glVertexPointer(2, GL_FLOAT, GLfloat.sizeof * 2, cast(void*)0);
Are you sure that vertices.sizeof is right? It can be wrong. Maybe you want
something like:
(vertices[0]).sizeof * vertices.length
That: cast(void*)0
is better written:
null
The sizeof of a dynamic array is 2 CPU words.
Bye,
bearophile
Apr 25 2010
Guilty on all charges. Confused the behaviour of static and dynamic arrays with sizeof. On 25/04/10 21:54, bearophile wrote:Bernard Helyer:glBufferData(GL_ARRAY_BUFFER, vertices.sizeof, vertices.ptr, GL_STATIC_DRAW); glVertexPointer(2, GL_FLOAT, GLfloat.sizeof * 2, cast(void*)0);Are you sure that vertices.sizeof is right? It can be wrong. Maybe you want something like: (vertices[0]).sizeof * vertices.length That: cast(void*)0 is better written: null The sizeof of a dynamic array is 2 CPU words. Bye, bearophile
Apr 25 2010