<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"> <head> <meta http-equiv="Content-Type" content="text/html; charset=us-ascii"> <meta name="Generator" content="Microsoft Word 15 (filtered medium)"> <style></style> </head> <body lang="IT" link="#0563C1" vlink="#954F72"> <div class="WordSection1"> Hi,<o:p></o:p> I’m new to this forum, but not to OpenGL and graphics.<o:p></o:p> I used to develop graphics (OpenGL) on Win for many years.<o:p></o:p> Recently I had to port my application to Linux, and there started many graphic issues.<o:p></o:p> Specifically, I’m using a VM Linux (CentOS 6.6) on a Pc.<o:p></o:p> <o:p> </o:p> When I check the OpenGL implementation in my application, this is what it returns:<o:p></o:p> Vendor : VMware, Inc.<o:p></o:p> Renderer : Gallium 0.4 on llvmpipe (LLVM 3.6, 256 bits)<o:p></o:p> Version : 2.1 Mesa 11.0.7<o:p></o:p> <o:p> </o:p> So, yes, on that VM Linux, it is using a software emulation (correct? I’ve read that LLVM is a software emulation).<o:p></o:p> The issue that I’m experiencing is about using glDrawElements in selection mode (glRenderMode(GL_SELECT)).<o:p></o:p> I could narrow down the issue till a very simple case, whose behavior I cannot explain.<o:p></o:p> In detail, this is the sample code I’m calling:<o:p></o:p> <o:p> </o:p> GLfloat faceNodes[12];<o:p></o:p> faceNodes[ 0] = 0.1; faceNodes[ 1] = 0.1; faceNodes[ 2] = 0.0; // index 0<o:p></o:p> faceNodes[ 3] = -0.1; faceNodes[ 4] = 0.1; faceNodes[ 5] = 0.0; // index 1<o:p></o:p> faceNodes[ 6] = -0.1; faceNodes[ 7] = -0.1; faceNodes[ 8] = 0.0; // index 2<o:p></o:p> faceNodes[ 9] = 0.1; faceNodes[10] = -0.1; faceNodes[11] = 0.0; // index 3<o:p></o:p> glVertexPointer(3, GL_FLOAT, 0, faceNodes);<o:p></o:p> <o:p> </o:p> GLuint auxTriaIndices[6];<o:p></o:p> auxTriaIndices[0] = 0;<o:p></o:p> auxTriaIndices[1] = 1;<o:p></o:p> auxTriaIndices[2] = 2;<o:p></o:p> auxTriaIndices[3] = 2;<o:p></o:p> auxTriaIndices[4] = 3;<o:p></o:p> auxTriaIndices[5] = 0;<o:p></o:p> glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, auxTriaIndices);<o:p></o:p> <o:p> </o:p> In GL_RENDER mode this code works fine. It renders a square made by 2 triangles (a top-left triangle, and a bottom-right triangle which share the diagonal of the square).<o:p></o:p> But when I’m in GL_SELECT mode, only the top-left triangle is picked. No OpenGL hit record triggered when I move my mouse onto the bottom-right triangle.<o:p></o:p> You’ve noticed that I’m using pure OpenGL 1.1 implementation, i.e. no VBO. But that should not be a problem (and in fact it renders correctly).<o:p></o:p> Furthermore, I tried to swap the indices of the 2 triangles in auxTriaIndices (i.e. from (0,1,2,2,3,0) to (2,3,0,0,1,2)), but it still picks the top-left triangle, and not the bottom-right. In short, it seems to me that it works like if I called: glDrawArrays(GL_TRIANGLES, 0, 6);<o:p></o:p> In fact it seems to ignore the second triangle (i.e. vertices 3,4,5 in the list ‘faceNode’, as nodes 4 and 5 are undefined), and only taking into count the first triangle.<o:p></o:p> As a further confirmation, I tried to add 2 additional vertices to ‘faceNode’. And it now selects as the second triangle the one defined by the vertices 3,4,5 in the list ‘faceNode’, regardless of the indices I pass to glDrawElements. How is that possible, as I’m using glDrawElements, in which I pass a list of indices?<o:p></o:p> And also, whay should it work in GL_RENDER mode, but not in GL_SELECT mode? BTW, above code works fine on Win, both using direct graphic board (an nVidia graphic card) or by software emulation (Microsoft GDI, which means OpenGL 1.1).<o:p></o:p> Any idea what might be wrong?<o:p></o:p> My code seems correct. Or not?<o:p></o:p> <o:p> </o:p> Thanks,<o:p></o:p> Gianluca <o:p></o:p> <o:p> </o:p> </div> </body> </html>