I am using GL_RGB10_A2UI internal format in glCopyTexImage1D() API but getting GL_INVALID_OPERATION error. Does OpenGL 3.3 support GL_RGB10_A2UI in glCopyTexImage1D() ?
GL_RGB10_A2UI is an integral image format; it contains integers, not normalized floating-point values that are stored as integers. Therefore, unless your framebuffer also contains unsigned integer values, this copy operation will fail with the expected error.
Of course, the only way for your framebuffer to have unsigned integers (rather than unsigned normalized integers, which is the usual case) would be to use an FBO. In which case, you could just be rendering directly to this texture, and you wouldn't need to copy from it.
I'm guessing you probably meant to use GL_RGB10_A2, which represent unsigned normalized values.
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Is there a fast way to clear an OpenGL buffer with a double-precision data type or set a default value with an API call to avoid using a compute shader?
For half- and single-precision types, glClearBufferData/glClearNamedBufferData can be used, but it appears like there is no internal format enum for 64 bit types, which makes the switch from single- to double-precision data in scientific computing applications more cumbersome. Or am I missing an extension?
I am looking for a solution that works with OpenGL 4.6, Nvidia-specific extensions are fine.
At the end of the day, a "double" is just a way of interpreting 64-bits of data. Your goal is to get the right 64-bits into your buffer.
As far as buffer clearing is concerned, the image format and pixel transfer parameters are just an explanation of how to interpret the data you pass. If the internal format of the clearing operation is GL_RG32UI, then each "pixel" in the buffer is 64-bits of data.
Given that, all you need to do is to get the clearing function to take a block of 64-bits and copy it exactly as you provide it. To do this, you have to use the right pixel transfer parameters.
See, pixel transfer operations can perform data conversion, taking the data pointer you pass and converting it to match the internal format. You don't want that; you want a direct copy. So your pixel transfer parameters need to exactly match the internal format. Which is quite easy.
A format of GL_RG_INTEGER represents a two-component pixel that stores integer data, in red-green order. And a type of GL_UNSIGNED_INT means that each component is a 32-bit unsigned integer. This exactly matches the internal format of GL_RG32UI, so the copying algorithm won't mess with the bytes of your data.
So, given some 64-bit double value in C or C++, clearing a buffer to that double ought to be as simple as:
void clear_buffer_to_double(GLuint buffer, double dbl)
{
glClearNamedBufferData(buffer, GL_RG32UI, GL_RG_INTEGER, GL_UNSIGNED_INT, &dbl);
}
glTexImage2D takes internalFormat (which specifies number of bits and data type/encoding), format (without number of bits and encoding) and type.
Is it possible, for example, to let OpenGL convert passed pixel data containing 32 bit integers from format GL_RGB_INTEGER and type GL_INT to internal format GL_RGB32F?
The wiki article https://www.khronos.org/opengl/wiki/Pixel_Transfer#Format_conversion suggests to me it's possible by stating:
Pixels specified by the user must be converted between the user-specified format (with format and type) and the internal representation controlled by the image format of the image.
But I wasn't able to read from floating point sampler in shader.
The _INTEGER pixel transfer formats are only to be used for transferring data to integer image formats. You are filling in a floating-point texture, so that doesn't qualify. You should have gotten an OpenGL Error.
Indeed, the very article you linked to spells this out:
Also, if "_INTEGER" is specified but the image format is not integral, then the transfer fails.
GL_RGBA32F is not an integral image format.
If you remove the _INTEGER part, then the pixel transfer will "work". OpenGL will assume that the integer data are normalized values, and therefore you will get floating-point values on the range [-1, 1]. That is, if you pass a 32-bit integer value of 1, the corresponding floating-point value will be 1/(2^31-1), which is a very small number (and thus, almost certainly just 0.0).
If you want OpenGL to cast the integer as if by a C cast (float)1... well, there's actually no way to do that. You'll just have to convert the data yourself.
The OpenGL documentation says very little about these two functions. When it would make sense to use glTexParameterIiv instead of glTexParameteriv or even glTexParameterfv?
If the values for GL_TEXTURE_BORDER_COLOR are specified with glTexParameterIiv or glTexParameterIuiv, the values are stored unmodified with an internal data type of integer. If specified with glTexParameteriv, they are converted to floating point with the following equation: f=(2c+1)/(2b−1). If specified with glTexParameterfv, they are stored unmodified as floating-point values.
You sort of answered your own question with the snippet you pasted. Traditional textures are fixed-point (unsigned normalized, where values like 255 are converted to 1.0 through normalization), but GL 3.0 introduced integral (signed / unsigned integer) texture types (where integer values stay integers).
If you had an integer texture and wanted to assign a border color (for use with the GL_CLAMP_TO_BORDER wrap mode), you would use one variant of those two functions (depending on whether you want signed or unsigned).
You cannot filter integer textures, but you can still have texture coordinate wrap behavior. Since said textures are integer and glTexParameteriv (...) normalizes the color values it is passed, an extra function had to be created to keep the color data integer.
You will find this same sort of thing with glVertexAttribIPointer (...) and so forth; adding support for integer data (as opposed to simply converting integer data to floating-point) to the GL pipeline required a lot of new commands.
Will the fragment shader automatically clamp the color value to its range?
Do I need to explicitly clam the value int he shader code?
If I do not, and the shader automatically does clampping, does it mean it will save some processing time?
Yes, they are clamped automatically if the color buffer is in a normalized fixed-point format. Copied from the OpenGL 3.3 spec:
Color values written by a fragment shader may be floating-point, signed integer, or unsigned integer. If the color buffer has an signed or unsigned normalized fixed-point format, color values are assumed to be floating-point and are converted to fixed-point as described in equations 2.6 or 2.4, respectively; otherwise no type conversion is applied.
The referenced section "Conversion from Floating-Point to Normalized Fixed-Point" says (emphasis added):
The conversion from a floating-point value f to the corresponding unsigned normalized fixed-point value c is defined by first clamping f to the range [0, 1], then ...
Explicitly clamping in the fragment shader would be a waste of operations if your frame buffer format is of a normalized fixed-point type (like the typical GL_RGBA8). Extra clamping operations in the shader would most likely be very cheap, but certainly unnecessary.
The situation is different if you use floating point color buffers. As implied by the spec quote above, no clamping is applied in this case. Which is expected, because one main motivation for using floating point color buffers is to have an extended range of values. Floating point color buffers are created by rendering to an FBO with an attachment type of GL_RGBA16F, GL_RGBA32F, or similar.
What is the advantage or need of integer and SNORM textures? when do we use (-1,0) range for textures?
Any example where we need specifically integer or SNORM textures?
According to https://www.opengl.org/registry/specs/EXT/texture_snorm.txt,
signed normalized integer texture formats are used to represent a floating-point values in the range [-1.0, 1.0] with an exact value of floating point zero.
It is nice for storing noise, especially Perlin.
Better than float textures because no bits wasted on the exponent.
Unfortunately, as of GL4.4 none of the snorm formats can be rendered to.
You can use the unorm formats and *2-1 for the same effect, although there may be issues with getting an exact 0.