[SOLVED] Question about simple render problem

C++ coding using Panda3D
1

hello,

how come this code works :

#include "pandaFramework.h"
#include "pandaSystem.h" 

#include "GeomNode.h"
#include "GeomTriangles.h"

PandaFramework framework;

WindowFramework *window;

float HALF_BOX_DIM = 10.0f;

const LVector3f gsBoxVertOffsets[8] =
{
	//top
	(-HALF_BOX_DIM, -HALF_BOX_DIM, HALF_BOX_DIM),
	(HALF_BOX_DIM, -HALF_BOX_DIM, HALF_BOX_DIM),
	(HALF_BOX_DIM, HALF_BOX_DIM, HALF_BOX_DIM),
	(-HALF_BOX_DIM, HALF_BOX_DIM, HALF_BOX_DIM),

	//bottom
	(-HALF_BOX_DIM, -HALF_BOX_DIM, -HALF_BOX_DIM),
	(HALF_BOX_DIM, -HALF_BOX_DIM, -HALF_BOX_DIM),
	(HALF_BOX_DIM, HALF_BOX_DIM, -HALF_BOX_DIM),
	(-HALF_BOX_DIM, HALF_BOX_DIM, -HALF_BOX_DIM)
};

int main(int argc, char *argv[]) 
{
	framework.open_framework(argc, argv);

	WindowProperties prop; 
	framework.get_default_window_props(prop); 
	prop.set_title("Test Panda 3D"); 
	prop.set_cursor_hidden(true); 

	window = framework.open_window(prop,0); 
	window->set_background_type(WindowFramework::BT_gray); 
	window->setup_trackball(); 

	PT(Geom) mVertexGeom;
	PT(GeomVertexData) mBoxVData;
	GeomVertexRewriter mBoxVertices;
	GeomVertexRewriter mBoxColors;

	mBoxVData = new GeomVertexData("Vertex", GeomVertexFormat::get_v3c4(), Geom::UH_dynamic);
	mBoxVertices = GeomVertexRewriter(mBoxVData, "vertex");
	mBoxColors = GeomVertexRewriter(mBoxVData, "color");

	mVertexGeom = new Geom(mBoxVData);

	LVector4f vertexColor(0 ,1.0f ,0 ,1.0f);



	//LVector3f v0 = gsBoxVertOffsets[0];
	//LVector3f v1 = gsBoxVertOffsets[1];
	//LVector3f v2 = gsBoxVertOffsets[2];

	LVector3f v0 = LVector3f(-HALF_BOX_DIM, -HALF_BOX_DIM, HALF_BOX_DIM);
	LVector3f v1 = LVector3f(HALF_BOX_DIM, -HALF_BOX_DIM, HALF_BOX_DIM);
	LVector3f v2 = LVector3f(HALF_BOX_DIM, HALF_BOX_DIM, HALF_BOX_DIM);

	mBoxVertices.add_data3f(v0);
	mBoxColors.add_data4f(vertexColor);
	mBoxVertices.add_data3f(v1);
	mBoxColors.add_data4f(vertexColor);
	mBoxVertices.add_data3f(v2);
	mBoxColors.add_data4f(vertexColor);


	PT(GeomTriangles) prim = new GeomTriangles(Geom::UH_dynamic);

	prim->add_vertex(0);
	prim->add_vertex(1);
	prim->add_vertex(2);

	prim->close_primitive();
	mVertexGeom->add_primitive(prim); 

	PT(GeomNode) pTestGeom = new GeomNode("TestBox");
	pTestGeom->add_geom(mVertexGeom);
	NodePath vertexNodePath = window->get_render().attach_new_node(pTestGeom);
	vertexNodePath.set_two_sided(true);
	vertexNodePath.show();


	framework.main_loop();


	framework.close_framework();  
	return (0);
}

but if this is used

	//LVector3f v0 = gsBoxVertOffsets[0];
	//LVector3f v1 = gsBoxVertOffsets[1];
	//LVector3f v2 = gsBoxVertOffsets[2];

instead of

	LVector3f v0 = LVector3f(-HALF_BOX_DIM, -HALF_BOX_DIM, HALF_BOX_DIM);
	LVector3f v1 = LVector3f(HALF_BOX_DIM, -HALF_BOX_DIM, HALF_BOX_DIM);
	LVector3f v2 = LVector3f(HALF_BOX_DIM, HALF_BOX_DIM, HALF_BOX_DIM);

it doesn’t seem to work ?

I can’t think of any reason why that would be different ?

Chrys

2

You have been tricked by a confusion about C++ syntax. Instead of this:

const LVector3f gsBoxVertOffsets[8] =
{
   //top
   (-HALF_BOX_DIM, -HALF_BOX_DIM, HALF_BOX_DIM),
   (HALF_BOX_DIM, -HALF_BOX_DIM, HALF_BOX_DIM),
   (HALF_BOX_DIM, HALF_BOX_DIM, HALF_BOX_DIM),
   (-HALF_BOX_DIM, HALF_BOX_DIM, HALF_BOX_DIM),

   //bottom
   (-HALF_BOX_DIM, -HALF_BOX_DIM, -HALF_BOX_DIM),
   (HALF_BOX_DIM, -HALF_BOX_DIM, -HALF_BOX_DIM),
   (HALF_BOX_DIM, HALF_BOX_DIM, -HALF_BOX_DIM),
   (-HALF_BOX_DIM, HALF_BOX_DIM, -HALF_BOX_DIM)
};

Write this:

const LVector3f gsBoxVertOffsets[8] =
{
   //top
   LVector3f(-HALF_BOX_DIM, -HALF_BOX_DIM, HALF_BOX_DIM),
   LVector3f(HALF_BOX_DIM, -HALF_BOX_DIM, HALF_BOX_DIM),
   LVector3f(HALF_BOX_DIM, HALF_BOX_DIM, HALF_BOX_DIM),
   LVector3f(-HALF_BOX_DIM, HALF_BOX_DIM, HALF_BOX_DIM),

   //bottom
   LVector3f(-HALF_BOX_DIM, -HALF_BOX_DIM, -HALF_BOX_DIM),
   LVector3f(HALF_BOX_DIM, -HALF_BOX_DIM, -HALF_BOX_DIM),
   LVector3f(HALF_BOX_DIM, HALF_BOX_DIM, -HALF_BOX_DIM),
   LVector3f(-HALF_BOX_DIM, HALF_BOX_DIM, -HALF_BOX_DIM)
};

The former does not mean the same thing as the latter. Instead, the C++ compiler interprets (-HALF_BOX_DIM, -HALF_BOX_DIM, HALF_BOX_DIM) as a single value evaluating to HALF_BOX_DIM (according to the rules of the comma operator), which it passes to the LVector3f constructor.

David

3

oh dear,

I’ve tried them all but at no point I was thinking the global data was “wrong”.

Cheers for that, I’ve learned something new there. :blush: