opengl beginner problems with glDrawElements

Graphics and GPU Programming Programming OpenGL

Started by hordak July 12, 2008 08:11 AM

0 comments, last by V-man 15 years, 9 months ago

122

Author

July 12, 2008 08:11 AM

Hi, I just started with OpenGL, so this question is certainly a silly one, but I hope it's easy to answer for a lot of you. I just started experimenting with OpenGL, and what I'm trying to do is drawing an indexed vertex array, which is just a simple cube. I took the vertices and indices from a blender x3d export and copied them into an array. I also evaluated the vertices and triangels on a paper and they should be correct. The result on the screen however is not much of a cube. It's a square and a few triangles pointing in weird directions. So here is the code of my draw method, any help would be highly appreciated. I guess there's something completely wrong with the way I thought drawing indexed primitives might work. Thank in advance. those guys are defined globally:



float cameraX = 4.0f;
#define DEGREES_TO_RADIANS(__ANGLE__) ((__ANGLE__) / 180.0 * M_PI)

and here's the drawing code, it draws a cube and updates the lookat to give a crappy flyby effect:



	const GLfloat cubeVertices[] = 
	{
		1, 1, -1, 
		1, -1, -1, 
		-1, -1, -1, 
		-1, 1, -1, 
		1, 1, 1, 
		1 -1, 1, 
		-1, -1, 1, 
		-1, 1, 1,		
	};
	
	const GLushort cubeIndices[] =
	{
		0, 1, 2, 
		0, 2, 3, 
		4, 7, 6, 
		4, 6, 5, 
		0, 4, 5,
		0, 5, 1, 
		1, 5, 6, 
		1, 6, 2, 
		2, 6, 7, 
		2, 7, 3, 
		4, 0, 3, 
		4, 3, 7, 		
	};
	
	const GLubyte squareColors[] = 
	{
		255, 255,   0, 255,
		0,   255, 255, 255,
		0,     0,   0,   0,
		255,   0, 255, 255,
		0,     0,   0,   0,
		255,   0, 255, 255,
		
		255, 255,   0, 255,
		0,   255, 255, 255,
		0,     0,   0,   0,
		255,   0, 255, 255,
		0,     0,   0,   0,
		255,   0, 255, 255,
		255, 255,   0, 255,
		0,   255, 255, 255,
		0,     0,   0,   0,
		255,   0, 255, 255,
		0,     0,   0,   0,
		255,   0, 255, 255,
		255, 255,   0, 255,
		0,   255, 255, 255,
		0,     0,   0,   0,
		255,   0, 255, 255,
		0,     0,   0,   0,
		255,   0, 255, 255,
		255, 255,   0, 255,
		0,   255, 255, 255,
		0,     0,   0,   0,
		255,   0, 255, 255,
		0,     0,   0,   0,
		255,   0, 255, 255,
		255, 255,   0, 255,
		0,   255, 255, 255,
		0,     0,   0,   0,
		255,   0, 255, 255,
		0,     0,   0,   0,
		255,   0, 255, 255,
		
	};	
	

	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();

	GLfloat	zNear = 0.1, zFar = 1000.0, fieldOfView = 60.0;
	GLfloat	size = 0;	
	size = zNear * tanf(DEGREES_TO_RADIANS(fieldOfView) / 2.0);
	
        glFrustum(-size, size, -size / (640.0f / 480.0f), size / (640.0f / 480.0f), zNear, zFar);
	
	cameraX -= 0.01f;
	
	gluLookAt(4.0f, cameraX, cameraX, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f);
	
	glMatrixMode(GL_MODELVIEW);
	
	glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
	
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
	
	glVertexPointer(3, GL_FLOAT, 0, cubeVertices);
	glEnableClientState(GL_VERTEX_ARRAY);
	
	
	glColorPointer(4, GL_UNSIGNED_BYTE, 0, squareColors);
	glEnableClientState(GL_COLOR_ARRAY);
	
	glDrawElements(GL_TRIANGLES, 36, GL_UNSIGNED_SHORT, cubeIndices);
	
	glFlush();

V-man

813

July 12, 2008 03:19 PM

It's because of the index list.

Here's some better code
http://www.geocities.com/vmelkon/glhlibrary.html

//HOW TO USE://glhCubeObject2 Cube;//memset(&Cube, 0, sizeof(glhCubeObject2));//Cube.Width=1.0; Cube.Height=1.0; Cube.Length=1.0;//Cube.WidthDivision=1; Cube.HeightDivision=1; Cube.LengthDivision=1;//Cube.AverageNormals=GL_FALSE;//Cube.IndexFormat=GLH_INDEXFORMAT_16BIT;//Cube.VertexFormat=GLHVERTEXFORMAT_VNT;//Cube.TexCoordStyle[0]=1;////glhCreateCubef2(&Cube);////HOW TO RENDER (You might want to use VBO, I'm just using VA here)://glEnable(GL_TEXTURE_2D);//glBindTexture(GL_TEXTURE_2D, TextureID);////glVertexPointer(3, GL_FLOAT, sizeof(GLHVertex_VNT), Cube.pVertex);//uint mypointer=(uint)Cube.pVertex;//mypointer+=12;//glNormalPointer(GL_FLOAT, sizeof(GLHVertex_VNT), (uint *)mypointer);//mypointer+=12;//glTexCoordPointer(2, GL_FLOAT, sizeof(GLHVertex_VNT), (uint *)mypointer);////glDrawRangeElements(GL_TRIANGLES, Cube.Start_DrawRangeElements, Cube.End_DrawRangeElements,//    Cube.TotalIndex, GL_UNSIGNED_SHORT, Cube.pIndex16Bit);////and to deallocate, call glhDeleteCubef2(&Cube);

Sig: http://glhlib.sourceforge.net
an open source GLU replacement library. Much more modern than GLU.
float matrix[16], inverse_matrix[16];
glhLoadIdentityf2(matrix);
glhTranslatef2(matrix, 0.0, 0.0, 5.0);
glhRotateAboutXf2(matrix, angleInRadians);
glhScalef2(matrix, 1.0, 1.0, -1.0);
glhQuickInvertMatrixf2(matrix, inverse_matrix);
glUniformMatrix4fv(uniformLocation1, 1, FALSE, matrix);
glUniformMatrix4fv(uniformLocation2, 1, FALSE, inverse_matrix);

opengl beginner problems with glDrawElements

This topic is closed to new replies.

Popular Topics

Recommended Tutorials

opengl beginner problems with glDrawElements

This topic is closed to new replies.

Popular Topics

Recommended Tutorials

Reticulating splines