Android opengl vertex array

Question

Simple question that i've always pondered about. When I first got into opengl I had to find a way to draw "tiles" or a bunch of triangles with 1 opengl draw call to improve performance vastly. I did that by putting all the vertices into an array and drawing the array. One problem that occurred was whenever I scrolled the tiles, I would see random placed pixels showing on and off depending on how much I scrolled the map. Around 5-8 on a 10x10 map. Now, I got back into opengl again and and this time I drew using GL_LINE_LOOP instead of GL_TRiANGLES. This never occurred to me back then but what I see when using GL_LINE_LOOP is all the triangles but when it finishes(it goes from bottom left to top right, so top right) there is a line connecting where I ended and where I began. Would the cause of those random pixels be because of this? Or does this have nothing to do with it. Does that line connecting the end and beginning appear because of GL_LINE_LOOP mode or does that also have nothing to do with and have to do with the way I created the map?

Answer 1

GL_LINE_LOOP is a completely different drawing mode - and no that won't be the reason why you're dropping pixels on tiles. Most likely reason for dropping pixels when drawing a tight mesh of tiles is that you're not computing the vertices consistently. The principle is that if a vertex is shared by two adjacent triangles (or quads, lines, whatever), then the floating point coordinates of that vertex must be 100% identical for every draw call. If you do that, then you're guaranteed to render a tight mesh without any gaps in between tiles. Your problem may have been something else though... perhaps Z fighting.. but my guess is the first thing I mention here.