GLCOPYCONVOLUTIONFILTER1D(3G)

📦 version 1.1, in centos-stream 9, fedora 43, fedora 44

🎀 NAME 🎀

okay so bestie, welcome to the GLCOPYCONVOLUTIONFILTER1D(3G) page — this is the 3G manual, and this whole page is about glCopyConvolutionFilter1D, which copies pixels into a one-dimensional convolution filter. that's the whole name, that's the whole vibe 💅

✨ C SPECIFICATION ✨

here's the signature, literally character for character, don't @ me:

void glCopyConvolutionFilter1D( GLenum target,
                                GLenum internalformat,
                                GLint x,
                                GLint y,
                                GLsizei width )

🌸 PARAMETERS 🌸

  • target — must be GL_CONVOLUTION_1D. that's it. that's the only option. it's giving "one job and it's doing it" 👑
  • internalformat — the internal format of the convolution filter kernel 🫶. the allowable values are GL_ALPHA, GL_ALPHA4, GL_ALPHA8, GL_ALPHA12, GL_ALPHA16, GL_LUMINANCE, GL_LUMINANCE4, GL_LUMINANCE8, GL_LUMINANCE12, GL_LUMINANCE16, GL_LUMINANCE_ALPHA, GL_LUMINANCE4_ALPHA4, GL_LUMINANCE6_ALPHA2, GL_LUMINANCE8_ALPHA8, GL_LUMINANCE12_ALPHA4, GL_LUMINANCE12_ALPHA12, GL_LUMINANCE16_ALPHA16, GL_INTENSITY, GL_INTENSITY4, GL_INTENSITY8, GL_INTENSITY12, GL_INTENSITY16, GL_R3_G3_B2, GL_RGB, GL_RGB4, GL_RGB5, GL_RGB8, GL_RGB10, GL_RGB12, GL_RGB16, GL_RGBA, GL_RGBA2, GL_RGBA4, GL_RGB5_A1, GL_RGBA8, GL_RGB10_A2, GL_RGBA12, or GL_RGBA16. yes that's a lot. yes you have to pick exactly one. no, you cannot freestyle ✨
  • x, y — the window space coordinates of the lower-left coordinate of the pixel array to copy 📍
  • width — the width of the pixel array to copy 📏

💖 DESCRIPTION 💖

so glCopyConvolutionFilter1D defines a one-dimensional convolution filter kernel using pixels from the current GL_READ_BUFFER — not from main memory, which is the whole plot twist vs glConvolutionFilter1D 😭

the screen-aligned pixel rectangle has its lower-left corner at (x, y), a width of width, and a height of 1, and that's what defines the convolution filter. and listen — if any pixels in that region are outside the window that's associated with the GL context, the values you get for those pixels are undefined. not "kinda weird", not "probably fine", undefined. act accordingly 🙈

the pixels in the rectangle get processed exactly as if glReadPixels had been called with format set to RGBA, but the process stops just before final conversion. then the R, G, B, and A components of each pixel are scaled by the four 1D GL_CONVOLUTION_FILTER_SCALE parameters and biased by the four 1D GL_CONVOLUTION_FILTER_BIAS parameters. (those scale and bias parameters are set by glConvolutionParameter using the GL_CONVOLUTION_1D target and the names GL_CONVOLUTION_FILTER_SCALE and GL_CONVOLUTION_FILTER_BIAS. the parameters themselves are vectors of four values that get applied to red, green, blue, and alpha — in that order, no shuffle.) and the R, G, B, and A values are not clamped to [0,1] at any time during this process. iconic behaviour honestly 🔥

each pixel is then converted to the internal format specified by internalformat. this conversion simply maps the component values of the pixel (R, G, B, and A) to the values included in the internal format (red, green, blue, alpha, luminance, and intensity). the mapping is as follows, and yes, every single row is here, we don't skip:

────────────────────────────────────────────────────────────────────────
Internal Format      Red   Green   Blue   Alpha   Luminance   Intensity
────────────────────────────────────────────────────────────────────────
GL_ALPHA                                    A
GL_LUMINANCE                                R
GL_LUMINANCE_ALPHA                  A       R
GL_INTENSITY                                                      R
GL_RGB                R      G      B
GL_RGBA               R      G      B       A
────────────────────────────────────────────────────────────────────────

so like, read it like a grid bestie: GL_ALPHA fills in alpha with A, GL_LUMINANCE fills luminance with R, GL_LUMINANCE_ALPHA fills alpha with A and luminance with R, GL_INTENSITY fills intensity with R, GL_RGB fills red/green/blue with R/G/B, and GL_RGBA fills red/green/blue/alpha with R/G/B/A 🌈

the red, green, blue, alpha, luminance, and/or intensity components of the resulting pixels are stored in floating-point rather than integer

ngl the source text literally stops right there mid-sentence 💀 i'm not gonna invent an ending for it, that's not my job, i just report what the page says.

pixel ordering is such that lower x screen coordinates correspond to lower i filter image coordinates 🦋

also heads up: after a convolution is performed, the resulting color components are also scaled by their corresponding GL_POST_CONVOLUTION_c_SCALE parameters and biased by their corresponding GL_POST_CONVOLUTION_c_BIAS parameters (where c takes on the values RED, GREEN, BLUE, and ALPHA). those parameters are set by glPixelTransfer. so like, the scaling never really ends, it's a whole journey ✨

⭐ NOTES ⭐

glCopyConvolutionFilter1D is present only if GL_ARB_imaging is returned when glGetString is called with an argument of GL_EXTENSIONS. so check first, bestie, don't just assume it's there 🫶

💀 ERRORS 💀

  • GL_INVALID_ENUM is generated if target is not GL_CONVOLUTION_1D.
  • GL_INVALID_ENUM is generated if internalformat is not one of the allowable values.
  • GL_INVALID_VALUE is generated if width is less than zero or greater than the maximum supported value. this value may be queried with glGetConvolutionParameter using target GL_CONVOLUTION_1D and name GL_MAX_CONVOLUTION_WIDTH.
  • GL_INVALID_OPERATION is generated if glCopyConvolutionFilter1D is executed between the execution of glBegin and the corresponding execution of glEnd. no mid-glBegin shenanigans, periodt 🚫

👑 ASSOCIATED GETS 👑

  • glGetConvolutionParameter
  • glGetConvolutionFilter

🦋 SEE ALSO 🦋

  • glConvolutionFilter1D(3G)
  • glConvolutionParameter(3G)
  • glPixelTransfer(3G)

and that's the whole page, bestie 💖 the footer is just GLCOPYCONVOLUTIONFILTER1D(3G) again — the 3G manual really said "same name, that's the whole footer", no extra version or date crumbs, and honestly? respect 💅✨🌸

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