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# OpenGL Interleaved Arrays w/ VBOs?

## 10 posts in this topic

I've been trying to get interleaved arrays working with core OpenGL for almost a day now, and nothing I try seems to work.  I dunno if it has to do with the offsets for my vertex attributes, the way I'm representing my data, or what.

I hate to dump code on you all, but I have to show it to you before I can explain what's going wrong:

/*
* Vertex declaration
*/
ke_vertexattribute_t va[] =
{
{ 0, 3, GL_FLOAT, No, 6*sizeof(float), 0 },
{ 1, 3, GL_FLOAT, No, 6*sizeof(float), 3*sizeof(float) },
{ -1, 0, 0, 0, 0, 0 },
};

/*
* Default vertex/fragment programs
*/
char default_vp[] =
"#version 150\n"
"in  vec3 in_pos;\n"
"in  vec3 in_colour;\n"
"out vec3 out_colour;\n"
"void main(void)\n"
"{\n"
"    gl_Position = vec4(in_pos, 1.0);\n"
"    out_colour = in_colour;\n"
"}\n";

char default_fp[] =
"#version 150\n"
"in vec3 out_colour;\n"
"out vec4 colour;\n"
"void main(void)\n"
"{\n"
"	colour = vec4(out_colour, 1.0);\n"
"}\n";

/*
* Working example
*/
GLfloat vertices[] =
{	-1.0f, -1.0f, 0.0f, 1.0f, 0.0f, 0.0f,
1.0f, -1.0f, 0.0f, 1.0f, 1.0f, 0.0f,
0.0f,  1.0f, 0.0f, 0.0f, 1.0f, 0.0f };

device = ke_create_renderdevice(&desc);
vb = new ke_ogl_vertexbuffer_t();
gp = new ke_ogl_gpu_program_t( default_vp, default_fp, NULL, NULL );

vb->set_buffer_data( sizeof( float ) * 18, vertices, No );

device->set_clear_colour_fv( colour );

while( index++ < 60000 )
{
device->clear_colour_buffer();
device->clear_depth_buffer();
device->set_program( gp );
device->set_vertex_buffer( vb );
device->set_vertex_attributes( va );
device->draw_vertices( GL_TRIANGLES, 0, 3 );
device->swap();
}

/*
* Name: ke_ogl_gpu_program_t::ke_ogl_gpu_program_t
* Desc: Initializes a GPU program with the shader sources of a vertex and fragment
*       program. Tesselation and geometry programs are optional.
*       TODO: Geometry and tesselation programs, allow user defined attribute locations.
*/
ke_ogl_gpu_program_t::ke_ogl_gpu_program_t( char* vertex_program, char* fragment_program, char* tesselation_program, char* geometry_program )
{
/* Set to uninitialized */
initialized = No;

GLuint p, f, v, t, g;

const char * vv = vertex_program;
const char * ff = fragment_program;

GLint compiled;

if (!compiled)
{
}

if (!compiled)
{
}

p = glCreateProgram();

glBindAttribLocation(p, 0, "in_pos");
glBindAttribLocation(p, 2, "in_normal");
glBindAttribLocation(p, 1, "in_colour");
glBindAttribLocation(p, 3, "in_tex1");
glBindAttribLocation(p, 4, "in_tex2");
glBindAttribLocation(p, 5, "in_tex3");
glBindAttribLocation(p, 6, "in_tex4");

glUseProgram(p);

program[0] = p;

initialized = Yes;
}

/*
* Name: ke_ogl_vertexbuffer::
* Desc:
*/
ke_ogl_vertexbuffer_t::ke_ogl_vertexbuffer_t()
{
/* Mark as uninitialized until the end */
initialized = No;

buffers[0] = 0;
buffers[1] = 0;

GLenum error = glGetError();

/* Generate vertex buffer object and array */
glGenVertexArrays( 1, &buffers[0] );
error = glGetError();

glGenBuffers( 1, &buffers[1] );
error = glGetError();

initialized = Yes;
}

void ke_ogl_vertexbuffer_t::set_buffer_data( uint32_t buffer_size, void* vertex_data, bool dynamic )
{
GLenum error = glGetError();

glBindVertexArray( buffers[0] );
error = glGetError();

glBindBuffer( GL_ARRAY_BUFFER, buffers[1] );
error = glGetError();

glBufferData( GL_ARRAY_BUFFER, buffer_size, vertex_data, dynamic ? GL_DYNAMIC_DRAW : GL_STATIC_DRAW );
error = glGetError();

glBindVertexArray(0);
}

/*
* Name: ke_ogl_renderdevice::set_vertex_buffer
* Desc: Sets the current vertex buffer to be used when rendering geometry.
*/
void ke_ogl_renderdevice_t::set_vertex_buffer( ke_vertexbuffer_t* vertexbuffer )
{
current_vertexbuffer = vertexbuffer;
}

void ke_ogl_renderdevice_t::set_program( ke_gpu_program_t* gpu_program )
{
/* Save a copy of this program */
current_gpu_program = gpu_program;

glUseProgram( ((uint32_t*)current_gpu_program->get_private_data())[0] );
}

void ke_ogl_renderdevice_t::set_vertex_attributes( ke_vertexattribute_t* vertex_attributes )
{
int i = 0;

/* Copy the vertex attributes */
while( vertex_attributes[i].index != -1 )
{
memmove( &current_vertexattribute[i], &vertex_attributes[i], sizeof( ke_vertexattribute_t ) );
i++;
}
}

/*
* Name: ke_ogl_renderdevice::draw_vertices
* Desc: Draws vertices from the current vertex buffer
*/
void ke_ogl_renderdevice_t::draw_vertices( uint32_t primtype, int first, int count )
{
GLenum error = glGetError();

/* Get a handle to the vertex array object */
uint32_t* buffers = (uint32_t*) current_vertexbuffer->get_private_data();

/* Bind the vertex array object and draw the vertices */
glBindVertexArray( buffers[0] );
error = glGetError();

glBindBuffer( GL_ARRAY_BUFFER, buffers[1] );
error = glGetError();

/* Set the vertex attributes before rendering */
for( int i = 0; current_vertexattribute[i].index != -1; i++ )
{
glVertexAttribPointer( current_vertexattribute[i].index,
current_vertexattribute[i].size,
current_vertexattribute[i].type,
current_vertexattribute[i].normalize,
current_vertexattribute[i].stride,
BUFFER_OFFSET( current_vertexattribute[i].offset ) );
glEnableVertexAttribArray(i);
}

glDrawArrays( primtype, first, count );
error = glGetError();
glBindVertexArray(0);
}


Okay, this is what goes on when I run this.  If I run this code the way it is, nothing shows up at all.  But if I comment out the 2nd line in my vertex declaration, like so:

/*
* Vertex declaration
*/
ke_vertexattribute_t va[] =
{
{ 0, 3, GL_FLOAT, No, 6*sizeof(float), 0 },
//    { 1, 3, GL_FLOAT, No, 6*sizeof(float), 3*sizeof(float) },
{ -1, 0, 0, 0, 0, 0 },
};


Then the triangle will render, but solid black.  I've checked the vertex attribute thing many times, and I can't see what's wrong with it.

And lastly, I don't want to limit my engine's rendering capabilities by only allowing multiple vertex buffers per attribute (especially since this is meant to be cross platform compatible with Direct3D), so I'm getting interleaved vertex attributes out of the way early.  Some say that there's likely to be a performance hit, but after doing a little reasearch, it's clear to me that interleaved vertex data works best when data is aligned properly (or is that only for OpenGL ES?).  Any ideas?  Thanks.

Shogun

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BUFFER_OFFSET( current_vertexattribute[i].offset )

What this is actually doing is taking the offset of your offset member and using that as the offset into your vertex format.  Just remove the BUFFER_OFFSET from it and it should work.

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Why are you using a vertex array object, and then rebinding your VBO and setting up the vertex attrib pointer every frame?

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If your vertex data is interleaved, then the offset between each vertex element will be sizeof of the all the vertex attributes for 1 vertex, thus a constant.

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If your vertex data is interleaved, then the offset between each vertex element will be sizeof of the all the vertex attributes for 1 vertex, thus a constant.

That's the stride, however, rather than the offset of each element, which is where the OP's problem is.

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If your vertex data is interleaved, then the offset between each vertex element will be sizeof of the all the vertex attributes for 1 vertex, thus a constant.

That's the stride, however, rather than the offset of each element, which is where the OP's problem is.

..correct and if the data is tightly packed then the stride is what is needed to make that function call do the same thing. Typical interleaved attributes are not sourced from different base pointer. rather each attribute is usually an offset from a common base. With that, the stride will be the offset between each attribute.

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If your vertex data is interleaved, then the offset between each vertex element will be sizeof of the all the vertex attributes for 1 vertex, thus a constant.

That's the stride, however, rather than the offset of each element, which is where the OP's problem is.

..correct and if the data is tightly packed then the stride is what is needed to make that function call do the same thing. Typical interleaved attributes are not sourced from different base pointer. rather each attribute is usually an offset from a common base. With that, the stride will be the offset between each attribute.

True, but it's still not the OP's problem.  If you check the posted code you'll see that the stride parameter is quite correct (6 * sizeof (float) for a vertex format of 6 floats) but the offsets are being specified wrong.

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BUFFER_OFFSET( current_vertexattribute[i].offset )

What this is actually doing is taking the offset of your offset member and using that as the offset into your vertex format.  Just remove the BUFFER_OFFSET from it and it should work.

First I wanted to say thanks for your response.  Second, I already tried removing that and replacing with

&current_vertexattribute[i].offset

instead, but that still doesn't work.  Is there another way to do this?

Why are you using a vertex array object, and then rebinding your VBO and setting up the vertex attrib pointer every frame?

Aren't VAOs required?  If they weren't, I'd gladly not use them as I find them to be a bit annoying sometimes.  Right now, I just want the stupid thing to work, even if it's wrong, so I can fix it afterwards.

Shogun.

EDIT: Fixed it.  The answer came to my mind the instant I woke up this morning.  I didn't copy the full contents in my vertex declaration/attribute structure.  The last element is important so that I know when to stop setting attributes.

 /* Copy the vertex attributes */
while( vertex_attributes[i].index != -1 )
{
memmove( &current_vertexattribute[i], &vertex_attributes[i], sizeof( ke_vertexattribute_t ) );
i++;
}

memmove( &current_vertexattribute[i], &vertex_attributes[i], sizeof( ke_vertexattribute_t ) );

So now it works, and the triangle is rendering just fine.  I left BUFFER_OFFSET in and it only appears to work with it.

Shogun.

Edited by blueshogun96
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Aren't VAOs required?  If they weren't, I'd gladly not use them as I find them to be a bit annoying sometimes.  Right now, I just want the stupid thing to work, even if it's wrong, so I can fix it afterwards.

VAOs are indeed required in modern OpenGL (well, at least in core profiles).

However, the whole point of VAO is to prevent you from having to rebind all your VBOs and attribute pointers every frame. You can set all that stuff up against the VBO once, and then just rebind the VAO by itself each time you need to draw.

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Interesting that it worked with BUFFER_OFFSET....

You asked if there is another way to do it; here's one that's not quite compatible with your setup, but works fine with MSVC in both C and C++, which I guess is relevant since you mentioned D3D compatibility; it may not be so robust or compatible elsewhere so use with appropriate caution.

struct vertextype
{
float position[3];
float normal[3];
};

vertextype *v = NULL;

glVertexAttribPointer (0, ..., v->position);
glVertexAttribPointer (1, ..., v->normal);

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