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_test.go

@@ -0,0 +1,88 @@
+package astiav_test
+
+import (
+	"testing"
+
+	"github.com/asticode/go-astiav"
+	"github.com/stretchr/testify/require"
+)
+
+func TestSoftwareScaleContext(t *testing.T) {
+	f1 := astiav.AllocFrame()
+	require.NotNil(t, f1)
+	defer f1.Free()
+
+	f2 := astiav.AllocFrame()
+	require.NotNil(t, f2)
+	defer f2.Free()
+
+	f3 := astiav.AllocFrame()
+	require.NotNil(t, f3)
+	defer f3.Free()
+
+	srcW := 320
+	srcH := 280
+	srcPixelFormat := astiav.PixelFormatYuv420P
+	dstW := 640
+	dstH := 480
+	dstPixelFormat := astiav.PixelFormatRgba
+	swscf1 := astiav.SoftwareScaleContextFlags(astiav.SoftwareScaleContextFlagBilinear)
+
+	f1.SetHeight(srcH)
+	f1.SetWidth(srcW)
+	f1.SetPixelFormat(srcPixelFormat)
+	require.NoError(t, f1.AllocBuffer(1))
+
+	swsc, err := astiav.CreateSoftwareScaleContext(srcW, srcH, srcPixelFormat, dstW, dstH, dstPixelFormat, swscf1)
+	require.NoError(t, err)
+	defer swsc.Free()
+
+	require.NoError(t, swsc.ScaleFrame(f1, f2))
+	require.Equal(t, dstH, f2.Height())
+	require.Equal(t, dstW, f2.Width())
+	require.Equal(t, dstPixelFormat, f2.PixelFormat())
+
+	dstW = 1024
+	dstH = 576
+	dstPixelFormat = astiav.PixelFormatYuv420P
+	swscf2 := astiav.SoftwareScaleContextFlags(astiav.SoftwareScaleContextFlagPoint)
+
+	require.Equal(t, swsc.Flags(), swscf1)
+	swsc.SetFlags(swscf2)
+	require.Equal(t, swsc.Flags(), swscf2)
+
+	require.NoError(t, swsc.SetSourceWidth(f2.Width()))
+	require.Equal(t, swsc.SourceWidth(), f2.Width())
+	require.NoError(t, swsc.SetSourceHeight(f2.Height()))
+	require.Equal(t, swsc.SourceHeight(), f2.Height())
+
+	newSourceW := 1280
+	newSourceH := 720
+	require.NoError(t, swsc.SetSourceResolution(newSourceW, newSourceH))
+	w, h := swsc.SourceResolution()
+	require.Equal(t, w, newSourceW)
+	require.Equal(t, h, newSourceH)
+	require.NoError(t, swsc.SetSourceResolution(f2.Width(), f2.Height()))
+	require.NoError(t, swsc.SetSourcePixelFormat(f2.PixelFormat()))
+	require.Equal(t, swsc.SourcePixelFormat(), f2.PixelFormat())
+
+	newDestW := 800
+	newDestH := 600
+	require.NoError(t, swsc.SetDestinationWidth(dstW))
+	require.Equal(t, swsc.DestinationWidth(), dstW)
+	require.NoError(t, swsc.SetDestinationHeight(dstH))
+	require.Equal(t, swsc.DestinationHeight(), dstH)
+	require.NoError(t, swsc.SetDestinationResolution(newDestW, newDestH))
+	w, h = swsc.DestinationResolution()
+	require.Equal(t, w, newDestW)
+	require.Equal(t, h, newDestH)
+	require.NoError(t, swsc.SetDestinationResolution(dstW, dstH))
+	require.NoError(t, swsc.SetDestinationPixelFormat(dstPixelFormat))
+	require.Equal(t, swsc.DestinationPixelFormat(), dstPixelFormat)
+
+	require.NoError(t, swsc.ScaleFrame(f2, f3))
+	require.Equal(t, dstW, f3.Width())
+	require.Equal(t, dstH, f3.Height())
+	require.Equal(t, dstPixelFormat, f3.PixelFormat())
+
+}