OpenGL ES - Pixel perfect image rendering?
Author
I'm making a kind of 3D music program mostly for entertainment value, using C# and OpenGL ES, targeting a Windows Mobile touchscreen smartphone (HTC Touch Diamond/Pro). I'm calling into Windows Media Player from my program. Everything is kind of sort of working.
I come from pre-existing 3D engines, so I'm just wondering what the best way to draw a pixel-precise image to the screen in OpenGL ES is - IE if I have a 64x64 bitmap and place it at 0, 0, I expect it to go from 0, 0 to 63, 63 and that's it. This way I can detect when the image has been touched - thus a bitmap button.
I tried using GDI, but it flickered terribly with the OpenGL rendering, even after placing the draw call after the OpenGL rendering was complete. It seems I will have to go with pure OpenGL for this task.
Does anyone have any pointers for me? Thanks.
[Edited by - AndyCR512 on December 1, 2008 9:19:05 AM]
Author
Thanks, though I tried that and couldn't get it to work. I think it's the .NET wrapper I'm using - it exposes things in a rather odd way (there's not even a glVertex3f function, for example - it has to be done with glVertexPointer and glDrawArrays), so I think I just need to figure out how the API would like me to do this. I got the wrapper here: http://www.koushikdutta.com/2008/08/net-compact-framework-wrapper-for.html
Quote:Original post by AndyCR512It is exposing things properly. Immediate mode (glVertex, etc.) is deprecated in OpenGL, and was intentionally never added to OpenGL ES.
I think it's the .NET wrapper I'm using - it exposes things in a rather odd way (there's not even a glVertex3f function, for example - it has to be done with glVertexPointer and glDrawArrays)
As for rendering GUI elements, you need to setup an orthographic projection matrix. Regular OpenGL includes a utility function for this, glOrtho(), but this was also removed from OpenGL ES, so you will have setup your own. Something like this should do the trick:
void setOrtho(float width, float height) { glMatrixMode(GL_PROJECTION); GLfloat m[16] = { 1.0f/width, 0, 0, 0, 0, 1.0f/height, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1 } glLoadMatrixf(m); glMatrixMode(GL_MODELVIEW);}This sets up an orthographic projection with the x axis aligned with the horizontal screen axis, from 0 to width, and the y-axis aligned with the vertical screen axis, from 0 to height. The only issue is that the y-axis may be inverted with respect to the screen's native coordinate system.
Author
Thank you for your help. The wrapper provides a glOrthox function for some reason, so I should be able to use that.
I still can't get it to work. I'll just keep trying. I feel so dumb being stuck on something as simple as drawing a bitmap. I think I spent too much time in high-level engines...
I still can't get it to work. I'll just keep trying. I feel so dumb being stuck on something as simple as drawing a bitmap. I think I spent too much time in high-level engines...
Quote:Original post by AndyCR512OK, so time for a quick check list:
I still can't get it to work. I'll just keep trying. I feel so dumb being stuck on something as simple as drawing a bitmap. I think I spent too much time in high-level engines...
- Have you created and loaded the texture?
- Is the texture set to use GL_NEAREST filtering?
- Is mipmapping disabled?
- Is the texture bound?
- Is texturing enabled?
- Does your quad have texture coordinates?
- Are the vertices of your quad in the right order (counter-clockwise)?
If you can answer yes to all of those, it should be working ;)
Author
Thanks. I get a perfect texture-mapped square when I try displaying in 3D. When I try displaying it on the screen so that it renders like a plain 2D bitmap, I get a muddy mess - presumably an extreme close-up of the center of the texture. I'll try disabling mipmapping and using GL_NEAREST.
I have a feeling it may have to do with how I'm submitting the vertex array - I use this:
gl.VertexPointer(3, gl.GL_FLOAT, 0, (IntPtr)trianglePointer);
I thought you're supposed to use integers to describe 2D triangles. However, the wrapper does not provide a gl.GL_INT constant.
I have a feeling it may have to do with how I'm submitting the vertex array - I use this:
gl.VertexPointer(3, gl.GL_FLOAT, 0, (IntPtr)trianglePointer);
I thought you're supposed to use integers to describe 2D triangles. However, the wrapper does not provide a gl.GL_INT constant.
Quote:Original post by AndyCR512That won't work. As you realised, you need a GL_INT constant to use an IntPtr, so since that is not available, specify your coordinates in floats instead.
I have a feeling it may have to do with how I'm submitting the vertex array - I use this:
gl.VertexPointer(3, gl.GL_FLOAT, 0, (IntPtr)trianglePointer);
I thought you're supposed to use integers to describe 2D triangles. However, the wrapper does not provide a gl.GL_INT constant.
Author
Thanks. I don't think that's passing an int - that pointer points to a float. The author of the wrapper used floats in his example, yet used IntPtr. Not at all sure why, but it seems to work.
I got it to kind of work by using smaller numbers in the vertices - .05 instead of 1, for instance. However, that does not correspond to one texel for one pixel on the screen. I don't know at all what these floats correspond to. Is it 0 for nothing and 1 to fill up the viewport? I'm just not sure.
At least it's displaying now, though scaled.
I got it to kind of work by using smaller numbers in the vertices - .05 instead of 1, for instance. However, that does not correspond to one texel for one pixel on the screen. I don't know at all what these floats correspond to. Is it 0 for nothing and 1 to fill up the viewport? I'm just not sure.
At least it's displaying now, though scaled.
Quote:Original post by AndyCR512It only corresponds to one texel-per-pixel if you have specified a projection matrix equivalent to glOrtho(0, width, 0, height), as in my earlier matrix function.
I got it to kind of work by using smaller numbers in the vertices - .05 instead of 1, for instance. However, that does not correspond to one texel for one pixel on the screen. I don't know at all what these floats correspond to. Is it 0 for nothing and 1 to fill up the viewport? I'm just not sure.
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