Implementation for SWS scale (#33)

* Draft implementation for SWS scale

* Update go.mod

* Revert "Update go.mod"

This reverts commit 760fb8c427.

* Renaming to AllocSwsContext and remove ChangeResolution this should handled by users

* update example to use new name and remove ChangeResolution

* Follow scaling example from libav, update readme, improve sws

Change scaling example to an similar libav example
Update readme
Add func to UpdateScalingParameters
Rename AllocSwsContext to SwsGetContext
Using a type for scaling algos/flags

* Fix Errors in scale example

* Review Changes

Now using sws context flags
Restructer sws context and adding ned simpler methods to update the ctx
Update the example
Update the test

* Correctly handle error for buffer alloc in PrepareDestinationFrameForScaling

* Add more getter and setter for sws

Get/Set source w,h,pixfmt
Get/Set dst w,h,pixfmt
Get/Set sws flags

* Adding resolution get/set

* Use CachedContext when updating sws ctx

* Review changes

Reorder flags, and update them
# Update Example
Use renaming function to create sws context
Clean up
Use new framdata image funcs
# Sws scale context
New way to update the context
Use sws_scale_frame instead of sws_scale
Reordering funcs for get and set
# Sws sclate context flag
Add "Flag" for algo name
# Update sws test

* fix fmt error args bug

* Review Changes

Simpfy sws update
Use c.int for sws flags
update test

software_scale_context.go

@@ -0,0 +1,203 @@
+package astiav
+
+//#cgo pkg-config: libswscale
+//#include <libswscale/swscale.h>
+import "C"
+import (
+	"errors"
+)
+
+// https://github.com/FFmpeg/FFmpeg/blob/n5.0/libswscale/swscale_internal.h#L300
+type SoftwareScaleContext struct {
+	c *C.struct_SwsContext
+	// We need to store attributes in GO since C attributes are internal and therefore not accessible
+	dstFormat C.enum_AVPixelFormat
+	dstH      C.int
+	dstW      C.int
+	flags     C.int
+	srcFormat C.enum_AVPixelFormat
+	srcH      C.int
+	srcW      C.int
+}
+
+type softwareScaleContextUpdate struct {
+	dstFormat *PixelFormat
+	dstH      *int
+	dstW      *int
+	flags     *SoftwareScaleContextFlags
+	srcFormat *PixelFormat
+	srcH      *int
+	srcW      *int
+}
+
+func CreateSoftwareScaleContext(srcW, srcH int, srcFormat PixelFormat, dstW, dstH int, dstFormat PixelFormat, flags SoftwareScaleContextFlags) (*SoftwareScaleContext, error) {
+	ssc := SoftwareScaleContext{
+		dstFormat: C.enum_AVPixelFormat(dstFormat),
+		dstH:      C.int(dstH),
+		dstW:      C.int(dstW),
+		flags:     C.int(flags),
+		srcFormat: C.enum_AVPixelFormat(srcFormat),
+		srcH:      C.int(srcH),
+		srcW:      C.int(srcW),
+	}
+
+	ssc.c = C.sws_getContext(
+		ssc.srcW,
+		ssc.srcH,
+		ssc.srcFormat,
+		ssc.dstW,
+		ssc.dstH,
+		ssc.dstFormat,
+		C.int(ssc.flags),
+		nil, nil, nil,
+	)
+	if ssc.c == nil {
+		return nil, errors.New("astiav: empty new context")
+	}
+	return &ssc, nil
+}
+
+func (ssc *SoftwareScaleContext) ScaleFrame(src, dst *Frame) error {
+	return newError(C.sws_scale_frame(ssc.c, dst.c, src.c))
+}
+
+func (ssc *SoftwareScaleContext) update(u softwareScaleContextUpdate) error {
+	dstW := ssc.dstW
+	if u.dstW != nil {
+		dstW = C.int(*u.dstW)
+	}
+
+	dstH := ssc.dstH
+	if u.dstH != nil {
+		dstH = C.int(*u.dstH)
+	}
+
+	dstFormat := ssc.dstFormat
+	if u.dstFormat != nil {
+		dstFormat = C.enum_AVPixelFormat(*u.dstFormat)
+	}
+
+	srcW := ssc.srcW
+	if u.srcW != nil {
+		srcW = C.int(*u.srcW)
+	}
+
+	srcH := ssc.srcH
+	if u.srcH != nil {
+		srcH = C.int(*u.srcH)
+	}
+
+	srcFormat := ssc.srcFormat
+	if u.srcFormat != nil {
+		srcFormat = C.enum_AVPixelFormat(*u.srcFormat)
+	}
+
+	flags := ssc.flags
+	if u.flags != nil {
+		flags = C.int(*u.flags)
+	}
+
+	c := C.sws_getCachedContext(
+		ssc.c,
+		srcW,
+		srcH,
+		srcFormat,
+		dstW,
+		dstH,
+		dstFormat,
+		flags,
+		nil, nil, nil,
+	)
+	if c == nil {
+		return errors.New("astiav: empty new context")
+	}
+
+	ssc.c = c
+	ssc.dstW = dstW
+	ssc.dstH = dstH
+	ssc.dstFormat = dstFormat
+	ssc.srcW = srcW
+	ssc.srcH = srcH
+	ssc.srcFormat = srcFormat
+	ssc.flags = flags
+
+	return nil
+}
+
+func (ssc *SoftwareScaleContext) Flags() SoftwareScaleContextFlags {
+	return SoftwareScaleContextFlags(ssc.flags)
+}
+
+func (ssc *SoftwareScaleContext) SetFlags(swscf SoftwareScaleContextFlags) error {
+	return ssc.update(softwareScaleContextUpdate{flags: &swscf})
+}
+
+func (ssc *SoftwareScaleContext) DestinationWidth() int {
+	return int(ssc.dstW)
+}
+
+func (ssc *SoftwareScaleContext) SetDestinationWidth(i int) error {
+	return ssc.update(softwareScaleContextUpdate{dstW: &i})
+}
+
+func (ssc *SoftwareScaleContext) DestinationHeight() int {
+	return int(ssc.dstH)
+}
+
+func (ssc *SoftwareScaleContext) SetDestinationHeight(i int) error {
+	return ssc.update(softwareScaleContextUpdate{dstH: &i})
+}
+
+func (ssc *SoftwareScaleContext) DestinationPixelFormat() PixelFormat {
+	return PixelFormat(ssc.dstFormat)
+}
+
+func (ssc *SoftwareScaleContext) SetDestinationPixelFormat(p PixelFormat) error {
+	return ssc.update(softwareScaleContextUpdate{dstFormat: &p})
+}
+
+func (ssc *SoftwareScaleContext) DestinationResolution() (width int, height int) {
+	return int(ssc.dstW), int(ssc.dstH)
+}
+
+func (ssc *SoftwareScaleContext) SetDestinationResolution(w int, h int) error {
+	return ssc.update(softwareScaleContextUpdate{dstW: &w, dstH: &h})
+}
+
+func (ssc *SoftwareScaleContext) SourceWidth() int {
+	return int(ssc.srcW)
+}
+
+func (ssc *SoftwareScaleContext) SetSourceWidth(i int) error {
+	return ssc.update(softwareScaleContextUpdate{srcW: &i})
+}
+
+func (ssc *SoftwareScaleContext) SourceHeight() int {
+	return int(ssc.srcH)
+}
+
+func (ssc *SoftwareScaleContext) SetSourceHeight(i int) error {
+	return ssc.update(softwareScaleContextUpdate{srcH: &i})
+}
+
+func (ssc *SoftwareScaleContext) SourcePixelFormat() PixelFormat {
+	return PixelFormat(ssc.srcFormat)
+}
+
+func (ssc *SoftwareScaleContext) SetSourcePixelFormat(p PixelFormat) error {
+	return ssc.update(softwareScaleContextUpdate{srcFormat: &p})
+}
+
+func (ssc *SoftwareScaleContext) SourceResolution() (int, int) {
+	return int(ssc.srcW), int(ssc.srcH)
+}
+
+func (ssc *SoftwareScaleContext) SetSourceResolution(w int, h int) error {
+	return ssc.update(softwareScaleContextUpdate{srcW: &w, srcH: &h})
+}
+
+func (ssc *SoftwareScaleContext) Free() {
+	if ssc.c != nil {
+		C.sws_freeContext(ssc.c)
+	}
+}