clearStencilBuffer();set zbuffer check to: lesser thanfor each surface do{  // init stencil check  set stencil: render only if stencilvalue = 0    // render surface, first pass  render surface without blending and write stencilvalue = 1  // update stencil check  set stencil: render only if stencilvalue = 1  // render surface, second pass  render surface with blending}

// For each image, I do:// Set-up stencil buffer pass. Don't update color or depth.// WRONG: you need to write the color//glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);glEnable(GL_STENCIL_TEST);// NOTE: render opaque part to background(stencil bit 1 = false) only !glStencilFunc(GL_EQUAL, 0x0, 0x1);glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);// Draw texture.drawTexture(image, pose);// Switch off writing of stencil buffer.// Switch on writing color (and depth).// NOTE: no need to set the color mask//glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);// NOTE: blend ontop of already drawn surfaces only (stencil bit 1 = true)//       if opaque has already been drawn in the first pass, you will  //       alpha blend the surface with itself which will not matterglStencilFunc(GL_EQUAL, 0x1, 0x1);glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);// In that region, alpha blending is enabled.glEnable(GL_BLEND);glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);// Draw texture.drawTexture(image, pose);// Disable blending.glDisable(GL_BLEND);glDisable(GL_STENCIL_TEST);