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    The behaviour of glMapBuffer is well-defined:...

    The behaviour of glMapBuffer is well-defined: https://www.opengl.org/sdk/docs/man2/xhtml/glMapBuffer.xml



    And also:



    That should be sufficient to answer your questions, but note in...
  2. You need to call glUseProgram before you can make...

    You need to call glUseProgram before you can make a glUniformMatrix call. Modern OpenGL also has glProgramUniform calls that don't need the glUseProgram.
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    Your usage of vertex attrib binding is fairly...

    Your usage of vertex attrib binding is fairly mixed up here, which is leading to this problem and will only cause you further issues later on. At a guess I'd say that you're porting from older...
  4. This is all normal, expected behaviour with this...

    This is all normal, expected behaviour with this kind of setup.

    You should use a texture array instead.
  5. As a general rule, if you encounter behaviour...

    As a general rule, if you encounter behaviour like this then you've either (rarely) found a driver bug, or (probably) have something wrong in your code.

    In your case it's your code. Look at your...
  6. An interesting quirk of OpenGL vs D3D is that in...

    An interesting quirk of OpenGL vs D3D is that in OpenGL if you specify a stride 0 it means that the data is tightly packed, whereas in D3D stride 0 means literally 0 and the data will repeat for each...
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    It's possible that your hardware doesn't support...

    It's possible that your hardware doesn't support any pixelformats which meet these requirements. You can do a loop over a DescribePixelFormat call (remembering that pixel formats are 1-based)...
  8. This is coming in Windows Server 2016, and is...

    This is coming in Windows Server 2016, and is available in the current preview version although I haven't personally tested it. See...
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    I don't see this happening. As Alfonse...

    I don't see this happening.

    As Alfonse suggests, the hardware would have to support it, otherwise the driver would punt you back to a software emulated mode, and becaue it's the depth buffer that...
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    Any particular reason why you're doing this...

    Any particular reason why you're doing this rather than using the builtin opengl32.lib?
  11. With GL 1.4 or the GL_ARB_texture_env_combine...

    With GL 1.4 or the GL_ARB_texture_env_combine extension (there's also an _EXT version but I'm ignoring that because _ARB is ubiquitous) you can set an RGB scaling factor of 1, 2 or 4 which is applied...
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    That's where the scissor test comes in - glClear...

    That's where the scissor test comes in - glClear obeys the current scissor test options, so for your initial example:
    You can use:
    glEnable (GL_SCISSOR_TEST);
    glScissor (1000, 800, 4, 4);...
  13. This is more of a theoretical problem than a...

    This is more of a theoretical problem than a practical one. In reality you're going to find that with n features you're not going to need every single combination, and that many combinations don't...
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    Try first calling glClearDepth to select the...

    Try first calling glClearDepth to select the value to clear it to.

    Then enable scissor test and set a scissor rect to the area to be cleared.

    Finally glClear (GL_DEPTH_BUFFER_BIT), and when...
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    But we still don't know what your problem is. ...

    But we still don't know what your problem is.

    OK, let me try to put this as clear as I can. You say you want to clear a polygon on the screen, but you haven't said why. You haven't told us what...
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    Actually if you look at the documentatio for it:...

    Actually if you look at the documentatio for it: https://www.opengl.org/sdk/docs/man2/xhtml/glOrtho.xml you'll see that the generated matrix uses division by "right - left", "top - bottom" and "far -...
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    At this stage you need to be more specific about...

    At this stage you need to be more specific about exactly what it is you're trying to do. Don't even focus on clearing stuff, forget about glScissor, forget about how you'd like to solve the problem,...
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    This is something that comes up regularly enough,...

    This is something that comes up regularly enough, although it's been a while since I've seen it.

    Typically somebody only wants to change a small part of the scene (maybe they're implementing an...
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    glOrtho ( Left , Left , 10.0 , 10.0 , ..... ...

    glOrtho ( Left , Left , 10.0 , 10.0 , .....
    This is almost certainly not what you want; see https://www.opengl.org/sdk/docs/man2/xhtml/glOrtho.xml
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    They look fine; I wouldn't worry about...

    They look fine; I wouldn't worry about deprecation in this case since glTexGen itself is also deprecated, so at least you've satisfied the condition that your calculations are going to be consistent.
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    You can use the GL specification to source the...

    You can use the GL specification to source the formulas used for texcoord auto-generation and recalculate them yourself from the retrieved vertex position value.
  22. Unfortunately OpenGL complicates things a little...

    Unfortunately OpenGL complicates things a little because the internalFormat you request is not necessarily what the driver itself will use.

    The classic example of this is that a GL_RGB...
  23. The driver will convert the format during the...

    The driver will convert the format during the transfer operation. Which could be slow.
  24. They're just different names for the same thing....

    They're just different names for the same thing.

    Modelling programs and D3D tend to use (u, v) whereas OpenGL tends to use (s, t) but it's just a naming convention. You could name them (x, y) or...
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    It's not necessarily going to perform faster if...

    It's not necessarily going to perform faster if you selectively update individual vector components like this. It may even perform slower.

    GPUs like reading each vertex as a contiguous chunk of...
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