我有一个渲染点流的程序。用于获取给定帧的点的方法具有强时间相干性，因此，在渲染循环中，首先，我使用计算着色器来压缩流，去除不需要的点。其次，我在集合中添加新点。最后，我使用glDrawElements渲染它。
这是执行该过程的代码（它使用Qt来操作OpenGL）：
template< typename Vec3 >
unsigned int CompactionRenderingState< Vec3 >::render()
{
// Compact stream.
m_nElements = compact();
// Sends new points to GPU.
QOpenGLBuffer* buffer = m_outputBuffers[ POS ];
buffer->bind();
buffer->write( m_nElements * BYTES_PER_VERTEX, ( void * ) &RenderingState::m_positions[ 0 ],
RenderingState::m_positions.size() * BYTES_PER_VERTEX );
buffer = m_outputBuffers[ ATTRIB0 ];
buffer->bind();
buffer->write( m_nElements * BYTES_PER_VERTEX, ( void * ) &RenderingState::m_colors[ 0 ],
RenderingState::m_colors.size() * BYTES_PER_VERTEX );
m_nElements += RenderingState::m_positions.size();
// Draws the resulting points.
m_arrayObj->bind();
unsigned int bufferOffset = 0;
switch( RenderingState::m_attribs )
{
case Attributes::NORMALS:
{
RenderingState::m_painter->setStandardEffect( QGL::LitMaterial );
m_outputBuffers[ POS ]->bind();
m_openGL->glVertexAttribPointer( QGL::Position, 3, GL_FLOAT, GL_FALSE, 0, &bufferOffset );
m_openGL->glEnableVertexAttribArray( QGL::Position );
m_outputBuffers[ ATTRIB0 ]->bind();
m_openGL->glVertexAttribPointer( QGL::Normal, 3, GL_FLOAT, GL_FALSE, 0, &bufferOffset );
m_openGL->glEnableVertexAttribArray( QGL::Normal );
break;
}
case Attributes::COLORS:
{
m_renderingProgram->bind();
m_outputBuffers[ POS ]->bind();
m_openGL->glVertexAttribPointer( QGL::Position, 3, GL_FLOAT, GL_FALSE, 0, &bufferOffset );
m_openGL->glEnableVertexAttribArray( QGL::Position );
m_outputBuffers[ ATTRIB0 ]->bind();
m_openGL->glVertexAttribPointer( QGL::Color, 3, GL_FLOAT, GL_FALSE, 0, &bufferOffset );
m_openGL->glEnableVertexAttribArray( QGL::Color );
break;
}
case Attributes::COLORS_AND_NORMALS:
{
throw logic_error( "Colors and normals not supported yet." );
break;
}
}
m_openGL->glMemoryBarrier( GL_VERTEX_ATTRIB_ARRAY_BARRIER_BIT );
m_openGL->glDrawArrays( GL_POINTS, 0, m_nElements );
m_openGL->glDisableVertexAttribArray( QGL::Position );
m_openGL->glDisableVertexAttribArray( QGL::Normal );
m_openGL->glDisableVertexAttribArray( QGL::Color );
m_openGL->glBindBuffer( GL_ARRAY_BUFFER, 0 );
m_renderingProgram->release();
m_arrayObj->release();
// Swaps buffers for the next frame.
for( int i = 0; i < N_BUFFER_TYPES; ++i )
{
std::swap( m_inputBuffers[ i ], m_outputBuffers[ i ] );
}
}
template< typename Vec3 >
unsigned int CompactionRenderingState< Vec3 >::compact()
{
// Makes the compaction of the unused points.
unsigned int nElements = m_compactionFlags.size();
unsigned int nBlocks = ( unsigned int ) ceil( ( float ) nElements / BLOCK_SIZE );
nElements = m_scan.doScan( m_compactionFlags );
m_openGL->glBindBufferBase( GL_SHADER_STORAGE_BUFFER, Scan::N_BUFFER_TYPES + POS, m_inputBuffers[ POS ]->bufferId() );
m_openGL->glBindBufferBase( GL_SHADER_STORAGE_BUFFER, Scan::N_BUFFER_TYPES + ATTRIB0,
m_inputBuffers[ ATTRIB0 ]->bufferId() );
m_openGL->glBindBufferBase( GL_SHADER_STORAGE_BUFFER, Scan::N_BUFFER_TYPES + N_BUFFER_TYPES + POS,
m_outputBuffers[ POS ]->bufferId() );
m_openGL->glBindBufferBase( GL_SHADER_STORAGE_BUFFER, Scan::N_BUFFER_TYPES + N_BUFFER_TYPES + ATTRIB0,
m_outputBuffers[ ATTRIB0 ]->bufferId() );
m_compactionProgram->bind();
m_compactionProgram->enableAttributeArray( "flags" );
m_compactionProgram->enableAttributeArray( "prefixes" );
m_compactionProgram->enableAttributeArray( "inputVertices" );
m_compactionProgram->enableAttributeArray( "inputAttrib0" );
m_compactionProgram->enableAttributeArray( "outputVertices" );
m_compactionProgram->enableAttributeArray( "outputAttrib0" );
m_openGL->glDispatchCompute( nBlocks, 1, 1 );
m_openGL->glMemoryBarrier( GL_SHADER_STORAGE_BARRIER_BIT );
m_compactionProgram->disableAttributeArray( "flags" );
m_compactionProgram->disableAttributeArray( "prefixes" );
m_compactionProgram->disableAttributeArray( "inputVertices" );
m_compactionProgram->disableAttributeArray( "inputAttrib0" );
m_compactionProgram->disableAttributeArray( "outputVertices" );
m_compactionProgram->disableAttributeArray( "outputAttrib0" );
m_openGL->glBindBuffer( GL_SHADER_STORAGE_BUFFER, 0 );
return nElements;
}
======编辑======
我已经编写了一个自动化测试来检查整个过程。该测试以这样的方式压缩点位置阵列和另一个属性，以便删除奇数索引中的数据。当我在gdb下运行禁用地址空间随机化的代码时，它会完美无缺地通过。但是，当在没有gdb的情况下运行或在gdb中启用了addres空间随机化时，返回的数组将全部为零，除非我在方法glDrawArrays中对render()进行评论。
======结束编辑======
TEST_F( CompactionTest, Compaction )
{
QGuiApplication app( g_argc, g_argv );
QSurfaceFormat format;
format.setVersion( 4, 3 );
format.setRenderableType( QSurfaceFormat::OpenGL );
format.setSwapBehavior( QSurfaceFormat::DoubleBuffer );
format.setSamples( 16 );
unsigned int nElements = 3000;
vector< unsigned int > flags( nElements );
vector< vec3 > pos( nElements );
vector< vec3 > attrib0( nElements );
for( int i = 0; i < nElements; ++i )
{
flags[ i ] = i % 2;
pos[ i ] = vec3( i, i, i );
attrib0[ i ] = vec3( i + nElements, i + nElements, i + nElements );
}
CompactionQGLView window( flags, pos, attrib0, format );
window.resize(640, 480);
window.show();
app.exec();
pos = window.m_compactedPos;
attrib0 = window.m_compactedAttrib0;
ASSERT_EQ( pos.size(), nElements * 0.5 );
ASSERT_EQ( attrib0.size(), nElements * 0.5 );
float expected = 1.;
for( int i = 0; i < pos.size(); ++i, expected += 2 )
{
vec3 expectedVec( expected, expected, expected );
cout << "Pos: " << pos[ i ] << ". Expected: " << expectedVec << endl;
ASSERT_EQ( pos[ i ], expectedVec );
expectedVec = vec3( expected + nElements, expected + nElements, expected + nElements );
cout << "Attrib0: " << attrib0[ i ] << ". Expected: " << expectedVec << endl << endl;
ASSERT_EQ( attrib0[ i ], expectedVec );
}
}
下一个函数读取压缩结果，并由测试中的window用于设置m_compactedPos和m_compactedAttrib0。
template< typename Vec3 >
vector< vector< Vec3 > > CompactionRenderingState< Vec3 >::getResultCPU()
{
m_openGL->glMemoryBarrier( GL_SHADER_STORAGE_BARRIER_BIT );
unsigned int resultSize = sizeof( Vec3 ) * m_nElements;
Vec3* result = ( Vec3* ) malloc( resultSize );
vector< vector< Vec3 > > results;
for( int i = 0; i < N_BUFFER_TYPES; ++i )
{
if( m_inputBuffers[ i ] != NULL )
{
m_openGL->glBindBuffer( GL_SHADER_STORAGE_BUFFER, m_inputBuffers[ i ]->bufferId() );
m_openGL->glGetBufferSubData( GL_SHADER_STORAGE_BUFFER, 0, resultSize, ( void * ) result );
vector< Vec3 > tempVec( m_nElements );
std::copy( result, result + m_nElements, tempVec.begin() );
results.push_back( tempVec );
}
}
free( result );
return results;
}
======编辑======
那么，只有在启用地址空间随机化时，才会出现此错误的可能原因？我被困住了，并且已经好几天试图解决这个问题了。有什么想法吗？
======结束编辑======
答案 0 :(得分：0)
最后，在调用glVertexAttribPointer时，问题是一个微妙的错误隐式类型转换。
void glVertexAttribPointer(GLuint index, GLint size, GLenum type, GLboolean normalized, GLsizei stride, const GLvoid * pointer)收到最后一个参数const GLvoid * pointer。在我的代码中，我将变量unsigned int bufferOffset的地址作为最后一个参数传递。这应该会导致OpenGL内部混乱。
要修复代码，我们只需要在glVertexAttribPointer函数的switch子句中更改render()次调用：
switch( RenderingState::m_attribs )
{
case Attributes::NORMALS:
{
RenderingState::m_painter->setStandardEffect( QGL::LitMaterial );
m_outputBuffers[ POS ]->bind();
m_openGL->glVertexAttribPointer( QGL::Position, 3, GL_FLOAT, GL_FALSE, 0, ( void * ) 0 );
m_openGL->glEnableVertexAttribArray( QGL::Position );
m_outputBuffers[ ATTRIB0 ]->bind();
m_openGL->glVertexAttribPointer( QGL::Normal, 3, GL_FLOAT, GL_FALSE, 0, ( void * ) 0 );
m_openGL->glEnableVertexAttribArray( QGL::Normal );
break;
}
case Attributes::COLORS:
{
m_renderingProgram->bind();
m_outputBuffers[ POS ]->bind();
m_openGL->glVertexAttribPointer( QGL::Position, 3, GL_FLOAT, GL_FALSE, 0, ( void * ) 0 );
m_openGL->glEnableVertexAttribArray( QGL::Position );
m_outputBuffers[ ATTRIB0 ]->bind();
m_openGL->glVertexAttribPointer( QGL::Color, 3, GL_FLOAT, GL_FALSE, 0, ( void * ) 0 );
m_openGL->glEnableVertexAttribArray( QGL::Color );
break;
}
case Attributes::COLORS_AND_NORMALS:
{
throw logic_error( "Colors and normals not supported yet." );
break;
}
}