Go binding for the cairo graphics library

Cairo has a get_current_point method that is not implemented here. I need it to implement a QuadraticCurveTo method, which does not exist in Cairo. It's trivial to create, but you need to factor in that initial point you are drawing from. I've done it in cairo-rs and would like to do the same here.

Was there a reason you chose not to implement that method?

System specs:

• Centos6
• Go 1.4.2
• cairo.x86_64 - 1.8.8-6.el6_6
• cairo-devel.x86_64 - 1.8.8-6.el6_6

when I run go-cairo-example I get the following output:

could not determine kind of name for C.cairo_pdf_version_t
could not determine kind of name for C.cairo_pdf_version_to_string

• added CreateLinearGradient
• added CreateRadialGradient
• added AddColorStopRGB
• added AddColorStopRGBA
• removed some returns that the linter was complaining about as unreachable code.

Sample Code:

surface := cairo.NewSurface(cairo.FORMAT_ARGB32, 400, 200)
pattern := cairo.CreateLinearGradient(0, 0, 200, 200)
pattern.AddColorStopRGB(0, 1, 1, 1)
pattern.AddColorStopRGB(1, 0, 0, 0)
surface.SetSource(pattern)
surface.Rectangle(0, 0, 200, 200)
surface.Fill()

pattern = cairo.CreateRadialGradient(300, 100, 0, 300, 100, 100)
pattern.AddColorStopRGB(0, 1, 0, 0)
pattern.AddColorStopRGB(1, 0, 0, 1)
surface.SetSource(pattern)
surface.Rectangle(200, 0, 200, 200)
surface.Fill()

Hi,

the last call to panic in surface.go seems to be misplaced, resulting in a runtime panic everytime cairo.NewSurfaceFromImage is called. This patch fixes the issue:

diff --git a/surface.go b/surface.go
index 3409279..9e1d655 100644
--- a/surface.go
+++ b/surface.go
@@ -724,6 +724,8 @@ func (self *Surface) SetImage(img image.Image) {

    case FORMAT_INVALID:
        panic("Invalid surface format")
+
+   default:
+       panic("Unknown surface format")
    }
-   panic("Unknown surface format")
 }

I am trying to use https://github.com/cheggaaa/go-poppler to extract images from pdf, but I am getting this during build: golang/src/github.com/cheggaaa/go-poppler/image.go:24: cannot use ci (type *C.struct__cairo_surface) as type *cairo.C.struct__cairo_surface in argument to cairo.NewSurfaceFromC golang/src/github.com/cheggaaa/go-poppler/image.go:24: cannot use ctx (type *C.struct__cairo) as type *cairo.C.struct__cairo in argument to cairo.NewSurfaceFromC

Do you have and idea how it can be fixed? I also filled issue there https://github.com/cheggaaa/go-poppler/issues/1 .

Without this change surface reference count remains > 0.

func (self *Surface) Destroy() {
+        C.cairo_destroy(self.context)
        C.cairo_surface_destroy(self.surface)
}

This change adds support for cairo_surface_write_to_png_stream, which allows a Surface to be written as a PNG to a byte buffer. Previously the only option for converting a Surface to a PNG was to write it to a file.

In function: GetImage()

The colors and alpha mask were reversed in FORMAT_ARGB32

FORMAT_RGB24 is actually 32 bit with 8 bits unused (and also in reverse order, just like FORMAT_ARGB32)

Pass in an unsafe.Pointer to the surface data. This allows for surfaces to be created e.g. from an SDL surface (would address #3):

package main

import (
	"time"
	"github.com/veandco/go-sdl2/sdl"
	"github.com/ungerik/go-cairo"
)

func main() {
	sdl.Init(sdl.INIT_EVERYTHING);
	defer sdl.Quit()

	window, _ := sdl.CreateWindow("test", sdl.WINDOWPOS_UNDEFINED, sdl.WINDOWPOS_UNDEFINED,
		800, 600, sdl.WINDOW_SHOWN)
	sdlSurface, _ := window.GetSurface()
	sdlSurface.FillRect(nil, 0)

	cairoSurface := cairo.NewSurfaceFromData(sdlSurface.Data(),
		cairo.FORMAT_ARGB32, int(sdlSurface.W), int(sdlSurface.H),
		int(sdlSurface.Pitch))
	cairoSurface.SelectFontFace("serif", cairo.FONT_SLANT_NORMAL, cairo.FONT_WEIGHT_BOLD)
	cairoSurface.SetFontSize(32.0)
	cairoSurface.SetSourceRGB(0.0, 0.0, 1.0)
	cairoSurface.MoveTo(10.0, 50.0)
	cairoSurface.ShowText("Hello World")
	cairoSurface.Finish()

	window.UpdateSurface()

	time.Sleep(5 * time.Second)
}

This adds hooks to C.cairo_get_current_point and C.cairo_has_current_point. These are vital for creating certain paths that are calculated from the current point, such as QuadraticCurveTo, which is not natively included in cairo.

The example/draw.go has two problems. The first, as outlined in another pull request, is the use of incorrect constants. The second problem is that it attempts to finish a surface before writing it out to a PNG. This is an invalid sequence of operations.

This patch fixes both of those issues.

i am building my project using below cmd. CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -o handlerBuild cmd/handler/main.go Error generated: imports github.com/ungerik/go-cairo: build constraints exclude all Go files in /home/oem/go/pkg/mod/github.com/ungerik/[email protected] can someone explain me, what is happening over here ?

my system details on which i am try to build.

GO111MODULE="auto"
GOARCH="amd64"
GOBIN="/home/oem/go/bin"
GOCACHE="/home/oem/.cache/go-build"
GOENV="/home/oem/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/oem/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/oem/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.19.3"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/oem/go/src/file-core/go.mod"
GOWORK=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build2645311516=/tmp/go-build -gno-record-gcc-switches"