OpenGL网格绘制显示错误

[abchappy1234]

不是很好描述这个问题，主要是这样的，下面的网格代码只能绘制255*255个格子的网格，多了就会出错。
初始化

m_iNumFaces = 0;	
m_iNumVertices = 0;		
m_iNumIndices = 0;

const int triangles_per_row = x_grids * 2;			// 一格两个三角形
const int indices_per_row = triangles_per_row + 2;

m_iNumVertices = (x_grids + 1) * (y_grids + 1);

m_pVertexArray = new meshVertex[m_iNumVertices];
if ( m_pVertexArray==NULL )			
	return false;

m_iNumIndices = indices_per_row * y_grids * 2;
m_pIndexArray = new unsigned short[m_iNumIndices];
if ( m_pIndexArray==NULL )
	return false;

m_iNumFaces = m_iNumIndices;

float x_adv = 1.0f/(float)(x_grids+1);	
float y_adv = 1.0f/(float)(y_grids+1);

int vertex_index = 0;
float fx, fy;
int x,y;

for ( y=0, fy=0; y<=y_grids; y++, fy+=y_adv )
{
	for ( x=0, fx=0; x<=x_grids; x++, fx+=x_adv, vertex_index++ )
	{
		// 坐标
		m_pVertexArray[vertex_index].m_Position[0] = fx*_width;
		m_pVertexArray[vertex_index].m_Position[1] = fy*_height;
		m_pVertexArray[vertex_index].m_Position[2] = 0.0f;
	}
}

const int vertices_per_row = x_grids + 1;
bool from_left_to_right = true;
int  index_index = 0;

// 生成索引
for ( y=0; y<y_grids; y++ )
{
	if ( from_left_to_right )
	{
		m_pIndexArray[index_index++] = y*vertices_per_row;

		for ( x=0; x<x_grids; x++ )
		{
			vertex_index = y * vertices_per_row + x;
			if ( x%2 == 0)		
			{
				m_pIndexArray[index_index++] = vertex_index + vertices_per_row;
				m_pIndexArray[index_index++] = vertex_index + vertices_per_row + 1;
				m_pIndexArray[index_index++] = vertex_index;
				m_pIndexArray[index_index++] = vertex_index + 1;
			}
			else			
			{
				m_pIndexArray[index_index++] = vertex_index;
				m_pIndexArray[index_index++] = vertex_index + 1;
				m_pIndexArray[index_index++] = vertex_index + vertices_per_row;
				m_pIndexArray[index_index++] = vertex_index + vertices_per_row + 1;
			}
		}
		m_pIndexArray[index_index++] = (x%2 == 0) ? vertex_index + 1 : vertex_index + 1 + vertices_per_row;
	}
	else
	{
		for ( x=x_grids; x>0; x-- )
		{
			vertex_index = y * vertices_per_row + x;
			if ( x%2 == 0)		
			{
				m_pIndexArray[index_index++] = vertex_index;
				m_pIndexArray[index_index++] = vertex_index - 1;
				m_pIndexArray[index_index++] = vertex_index + vertices_per_row;
				m_pIndexArray[index_index++] = vertex_index + vertices_per_row - 1;
			}
			else				
			{
				m_pIndexArray[index_index++] = vertex_index + vertices_per_row;
				m_pIndexArray[index_index++] = vertex_index + vertices_per_row - 1;
				m_pIndexArray[index_index++] = vertex_index;
				m_pIndexArray[index_index++] = vertex_index - 1;
			}
		}
		m_pIndexArray[index_index++] = vertex_index + vertices_per_row - 1;
	}
	from_left_to_right = !from_left_to_right;
}

绘制的时候就很简单

glPushClientAttrib(GL_CLIENT_VERTEX_ARRAY_BIT);

glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(3, GL_FLOAT, sizeof(meshVertex), m_pVertexArray);
// 用 GL_LINE_STRIP 看得错误会更明显
glDrawElements(GL_TRIANGLE_STRIP, m_iNumFaces, GL_UNSIGNED_SHORT, m_pIndexArray);
glPopClientAttrib();

[xingzhe2001]

你的index是16位的，最多也就是65535个索引，而256*256=65535刚好是极限，再多就索引出错了，改用32位索引就可以了

[xingzhe2001]

改为32位索引的方法是index array用unsigned int 类型，glDrawElement的第三个参数用 GL_UNSIGNED_INT

[张赐]

恩，index的范围太小了

[abchappy1234]

。。。。我晕，没注意