# Point Sprites **URL:** \ **Category:** PowerVR Insider\ **Created:** [November 25, 2010, 8:54am UTC](https://forums.imgtec.com/t/point-sprites/926 "2010-11-25T08:54:05Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![alvalea](https://sea1.discourse-cdn.com/flex015/user_avatar/forums.imgtec.com/alvalea/32/81_2.png) [@alvalea](https://forums.imgtec.com/u/alvalea)\ **Post date:** [November 25, 2010, 8:54am UTC](https://forums.imgtec.com/t/point-sprites/926/1 "2010-11-25T08:54:05Z")
Hi, I’m trying to do a particles system with point sprites. But I’ve got an error in the windows emulator when I use the gl\_PointCoord variable. The output is: "Fragment shaders uses varying gl\_TexCoord but vertex shader does not write to it." The source code of my shaders is the following: [vertex shader] attribute highp   vec4 inVertex; uniform mediump mat4 MVPMatrix; void main() {      gl\_PointSize = 200.0;      gl\_Position = MVPMatrix \* inVertex; } [fragment shader] uniform sampler2D sTexture; void main() {     gl\_FragColor = texture2D(sTexture, gl\_PointCoord); } As a first approach I was only trying to draw a textured point on the screen:         GLfloat vertex[] = {0.0f,0.0f,0.0f};      glEnableVertexAttribArray(VERTEX\_ARRAY);      glVertexAttribPointer (VERTEX\_ARRAY, 4, GL\_FLOAT, GL\_FALSE, 0, vertex);            glDrawArrays(GL\_POINTS, 0, 1); If I use a vec2 coordinate instead of the gl\_PointCoord, it draws a point sprite with uniform color. But with the gl\_PointCoord it fails. Am I missing something? Thanks ---
**Author:** ![martin-kraus](https://avatars.discourse-cdn.com/v4/letter/m/85f322/32.png) [@martin-kraus](https://forums.imgtec.com/u/martin-kraus)\ **Post date:** [November 26, 2010, 8:59am UTC](https://forums.imgtec.com/t/point-sprites/926/2 "2010-11-26T08:59:20Z")
Hi alvalea, strange error. What is your hardware? Do you know which OpenGL version and which extensions your driver supports? Could you try this fragment shader: void main()                        {                                            gl\_FragColor = vec4(gl\_PointCoord.x, gl\_PointCoord.y, 0.0, 1.0); }                                        ---
**Author:** ![alvalea](https://sea1.discourse-cdn.com/flex015/user_avatar/forums.imgtec.com/alvalea/32/81_2.png) [@alvalea](https://forums.imgtec.com/u/alvalea)\ **Post date:** [November 29, 2010, 8:59am UTC](https://forums.imgtec.com/t/point-sprites/926/3 "2010-11-29T08:59:36Z")
I’m trying it with an Intel integrated chip Q45/Q43. The supported OpenGL version is 2.0. The gl\_PointCoord coordinates are always (0,0). ---
**Author:** ![martin-kraus](https://avatars.discourse-cdn.com/v4/letter/m/85f322/32.png) [@martin-kraus](https://forums.imgtec.com/u/martin-kraus)\ **Post date:** [November 29, 2010, 11:52am UTC](https://forums.imgtec.com/t/point-sprites/926/4 "2010-11-29T11:52:33Z")
Strange. Well, "gl\_PointCoord" is a feature of GLSL 1.20; thus, you might have to add the line #version 120 at the start of your fragment shader. (Of course, you should also check whether GLSL 1.20 is supported on your hardware/driver. OpenGL 2.0 only requires GLSL 1.10; thus, this might be an issue.) If this doesn't work, I would suggest that you try to get the fragment shader to work in (desktop) OpenGL. If it doesn't work in (desktop) OpenGL on your hardware/driver, I would assume that it also doesn't work in the OpenGL ES emulator. (In desktop OpenGL you probably have to glEnable GL\_POINT\_SPRITE and GL\_VERTEX\_PROGRAM\_POINT\_SIZE but apart from this, the code should be very similar.) If the code works in (desktop) OpenGL but not in the OpenGL ES emulator, I would assume it's a bug in the emulator. :/ Martin Kraus2010-11-29 13:02:17 ---
**Author:** ![alvalea](https://sea1.discourse-cdn.com/flex015/user_avatar/forums.imgtec.com/alvalea/32/81_2.png) [@alvalea](https://forums.imgtec.com/u/alvalea)\ **Post date:** [November 30, 2010, 11:56am UTC](https://forums.imgtec.com/t/point-sprites/926/5 "2010-11-30T11:56:36Z")
If I add the line ‘#version 120’ the function PVRTShaderLoadFromFile fails. I guess that the problem is that the hardware doesn’t support GLSL 1.20. I will try to test it in another hardware. ---
**Author:** ![martin-kraus](https://avatars.discourse-cdn.com/v4/letter/m/85f322/32.png) [@martin-kraus](https://forums.imgtec.com/u/martin-kraus)\ **Post date:** [November 30, 2010, 1:35pm UTC](https://forums.imgtec.com/t/point-sprites/926/6 "2010-11-30T13:35:57Z")
alvelea, I just tested it and the OpenGL ES emulator seems to reject anything but version “#version 100”. Actually, GLSL version 1.00 for OpenGL ES appears to be based on GLSL version 1.20 for OpenGL. Thus, I guess you have to make sure to run the emulator on hardware that supports GLSL 1.20. ---
**Author:** ![alvalea](https://sea1.discourse-cdn.com/flex015/user_avatar/forums.imgtec.com/alvalea/32/81_2.png) [@alvalea](https://forums.imgtec.com/u/alvalea)\ **Post date:** [November 30, 2010, 3:51pm UTC](https://forums.imgtec.com/t/point-sprites/926/7 "2010-11-30T15:51:34Z")
Ok, thanks a lot 🙂