cgo | cgo by example

I'm trying to create a go program and I need to use freetype, but module for freetype in go seems really different from the original freetype library for c. Overcome this problem I created a simple library in C, and I'm trying to call a function in that library from Go using cgo. But I couldn't seem to figure out where should my .a file needs to be located in order go to be able to find it. I'm using go modules and my project is not in the GOPATH.

So my question is where I need to put my C library's .h and .a files?

I have a lib, that uses some C on linux. On windows it is just a dummy noop lib with functions that do nothing.

The lib is in 3 files: lib_linux.go, lib_win.go and lib.c

But when I try to compile it on windows, it throws this error: C source files not allowed when not using cgo or SWIG: lib.c

How can I tell to the go compiler to ignore the C source files on windows?

So I want to make a app that shows some images and when the window resizes, it scales also all images to fit on the screen. My strategy is this:

1. call clCreateImage for every original image and store the cl_mem pointers in a global map (something like: filename -> cl_mem)
2. call scale(cl_mem img, int width, int height), that calls a kernel and reads the output image data. Then show the scaled images.
3. when the a window resize event occures: drop all scaled images and call scale(...) another time, with the cl_mem pointers stored in the map

I tried it on a small scale where I just create one image, and call scale two times. The first is OK and scaled, but the second is corrupted. I don't know why, the src image is CL_MEM_READ_ONLY | CL_MEM_COPY_HOST_PTR, the out image is created in scale function.

original: https://ibb.co/pQDwScW

first time scaled (to fit in 300x300): https://ibb.co/nnN9kTY

second try (to fit in 500x500): https://ibb.co/561SkSn

But also when I try just 300x300 and then also 300x300 it is corrupted. Is there a rule, that images can't be used in a kernel multiple times? Or im just missing something?

EDIT:

C code is here: https://pastebin.com/NpSaxRyT

It is used from golang with cgo, so the createImage returns the cl_mem as void*, so that the Go part doesn't need to include cl.h.

init() function is called on startup of the Go program. createImage function is called from Go with pixel data.

So the image pointers (cl_mem pointers) are in Go and then the resize (scale) function is called. It takes the void* pointer and buffer pointer where the pixel data will be transfered. Also the buffer is allocated by Go, but with the first image it is OK and I think that the GC doesn't kick in (also tried to disable GC entirely).

like so:

In my project, I am using callbacks for bi-directional calls from C into go and vice versa using CGO. I resolved the issue of circular dependencies by compiling the C part into a library, then compiling the go part into a library, then a final linker pass puts it all together. This is working fine when not using go modules. Go source files are listed on the command line explicitly. I have been told that as of go 1.12 "this is not the right way to do it".

As the project has grown, I now want to use go modules. Unfortunately, this changes the behaviour of the go compiler. It now wants to resolve external dependencies and implicitly includes them in the output file. Due to the circular dependency, it now always ends up with an undefined reference or multiple definitions. How to resolve circular dependencies when using cgo and go modules "the right way"?

This is a minimal example to illustrate the problem. Remove the file-name "hello.go" from the call to go in the Makefile to see how it falls apart.

This is the error message:

I am trying to build my Rust crate as static lib to furter use it within Golang through FFI. So far tried buch of different approaches regarding linking, but still having undefined reference kind error from final go binary:

I am trying to run a simple go code

I am trying to use CGO to use realsense2.dll (Intel's RealSense camera library). I am on Windows 11 x64.

My test program that counts the number of devices connected works when my directory layout is:

• rs2test
  • go.mod
  • realsense2.dll
  • context.go (wrapper for C code)
  • devicelist.go (wrapper for C code)
  • error.go (wrapper for C code)
  • main.go

and in each wrapper for C code file I have the following directives:

My app compiles fine when GOARCH is set to arm64 (or is omitted). However, when I try to compile an amd64 binary (GOOS=darwin GOARCH=amd64 go build), I get the following error:

How to pass a string as argument from Python to a Go Dll using ctypes:

Go-code: