feature: read/write transparency (alpha) property on fills

[scanny]

No description provided.

[liuming]

Hi @scanny I wonder what it takes to support this feature. I'd like to help and possibility provide a PR if you can point me a direction.

[scanny]

Probably the easiest place to start is to create a single slide presentation having a single shape on it, then set the transparency, save, and inspect the XML. You should find an <a:alpha> element in the shape XML and that "specimen" will give most of the initial information needed.

There is some preliminary analysis here: http://python-pptx.readthedocs.io/en/latest/dev/analysis/dml-fill.html and here: http://python-pptx.readthedocs.io/en/latest/dev/analysis/dml-color.html

It looks like the MS API has a .Transparency property on FillFormat, so that's a pretty solid indication that's where we should do it too: https://github.com/scanny/python-pptx/blob/master/pptx/dml/fill.py#L20

opc-diag is handy for inspecting the XML. http://opc-diag.readthedocs.io/en/latest/

Why don't you have a look at these items and then you can ask any more specific questions you have :)

[keithcsqueensu]

Transparency options from PowerPoint's Format Shape GUI

The Format Shape pane contains the following Fill strategies.

In this comment, I will explore each of the Fill strategies and see how transparency works for each.

1. Solid Fill

1. Create a new pptx file with a blank slide.
2. Set slide layout to Blank
3. Insert a rectangle on the slide. This results to the file before.pptx.
4. I've set the transparency of that rectangle to 55%, resulting to the file solidFillTrans.pptx with the following modifications:

--- before/ppt/slides/slide1.xml

+++ solidFillTrans/ppt/slides/slide1.xml

@@ -39,6 +39,11 @@

           <a:prstGeom prst="rect">
             <a:avLst/>
           </a:prstGeom>
+          <a:solidFill>
+            <a:schemeClr val="accent1">
+              <a:alpha val="45000"/>
+            </a:schemeClr>
+          </a:solidFill>
         </p:spPr>
         <p:style>
           <a:lnRef idx="2">

The above is the Scheme Color only. I've created solidFillTransYellow.pptx with yellow color:

--- before/ppt/slides/slide1.xml

+++ solidFillTransYellow/ppt/slides/slide1.xml

@@ -39,6 +39,11 @@

           <a:prstGeom prst="rect">
             <a:avLst/>
           </a:prstGeom>
+          <a:solidFill>
+            <a:srgbClr val="FFFF00">
+              <a:alpha val="45000"/>
+            </a:srgbClr>
+          </a:solidFill>
         </p:spPr>
         <p:style>
           <a:lnRef idx="2">

2. No Fill

1. Start from before.pptx, change fill of rectangle to NoFill, resulting to the file noFillOrig.pptx with the following modifications:

--- before/ppt/slides/slide1.xml

+++ noFillOrig/ppt/slides/slide1.xml

@@ -39,6 +39,7 @@

           <a:prstGeom prst="rect">
             <a:avLst/>
           </a:prstGeom>
+          <a:noFill/>
         </p:spPr>
         <p:style>
           <a:lnRef idx="2">

2. There's no GUI option to change transparency.

3. Gradient Fill

1. Start from before.pptx, change fill to Gradient, resulting to gradFillOrig.pptx:

--- before/ppt/slides/slide1.xml

+++ gradFillOrig/ppt/slides/slide1.xml

@@ -39,6 +39,35 @@

           <a:prstGeom prst="rect">
             <a:avLst/>
           </a:prstGeom>
+          <a:gradFill>
+            <a:gsLst>
+              <a:gs pos="0">
+                <a:schemeClr val="accent1">
+                  <a:lumMod val="5000"/>
+                  <a:lumOff val="95000"/>
+                </a:schemeClr>
+              </a:gs>
+            
  <a:gs pos="74000">
+                <a:schemeClr val="accent1">
+                  <a:lumMod val="45000"/>
+                  <a:lumOff val="55000"/>
+                </a:schemeClr>
+              </a:gs>
+              <a:gs pos="83000">
+                <a:schemeClr val="accent1">
+                 
 <a:lumMod val="45000"/>
+                  <a:lumOff val="55000"/>
+                </a:schemeClr>
+              </a:gs>
+              <a:gs pos="100000">
+                <a:schemeClr val="accent1">
+                  <a:lumMod val="30000"/>
+                  <a:lumOff val="70000"/>
+              
  </a:schemeClr>
+              </a:gs>
+            </a:gsLst>
+            <a:lin ang="5400000" scaled="1"/>
+          </a:gradFill>
         </p:spPr>
         <p:style>
           <a:lnRef idx="2">

2. Add 44% transparency to Gradient Step 0, resulting to gradFillTrans.pptx:

--- gradFillOrig/ppt/slides/slide1.xml

+++ gradFillTrans/ppt/slides/slide1.xml

@@ -45,6 +45,7 @@

                 <a:schemeClr val="accent1">
                   <a:lumMod val="5000"/>
                   <a:lumOff val="95000"/>
+                  <a:alpha val="56000"/>
                 </a:schemeClr>
               </a:gs>
               <a:gs pos="74000">

4. Blip Fill

1. Start from before.pptx, change fill to Picture / Texture Fill. Turn off "Tile picture as texture" and "Rotate with Shape". Resulting to blipFillOrig.pptx:

--- before/ppt/slides/slide1.xml

+++ blipFillOrig/ppt/slides/slide1.xml

@@ -39,6 +39,13 @@

           <a:prstGeom prst="rect">
             <a:avLst/>
           </a:prstGeom>
+          <a:blipFill dpi="0" rotWithShape="0">
+            <a:blip r:embed="rId2"/>
+            <a:srcRect/>
+            <a:stretch>
+              <a:fillRect/>
+            </a:stretch>
+          </a:blipFill>
         </p:spPr>
         <p:style>
           <a:lnRef idx="2">

2. Add 55% transparency, resulting to blipFillTrans.pptx:

--- blipFillOrig/ppt/slides/slide1.xml

+++ blipFillTrans/ppt/slides/slide1.xml

@@ -40,7 +40,9 @@

             <a:avLst/>
           </a:prstGeom>
           <a:blipFill dpi="0" rotWithShape="0">
-            <a:blip r:embed="rId2"/>
+            <a:blip r:embed="rId2">
+              <a:alphaModFix amt="45000"/>
+            </a:blip>
             <a:srcRect/>
             <a:stretch>
               <a:fillRect/>

5. Pattern Fill

1. Start from before.pptx, change fill to Pattern Fill, resulting to pattnFillOrig.pptx:

--- before/ppt/slides/slide1.xml

+++ pattnFillOrig/ppt/slides/slide1.xml

@@ -39,6 +39,14 @@

           <a:prstGeom prst="rect">
             <a:avLst/>
           </a:prstGeom>
+          <a:pattFill prst="pct5">
+            <a:fgClr>
+              <a:schemeClr val="accent1"/>
+            </a:fgClr>
+            <a:bgClr>
+              <a:schemeClr val="bg1"/>
+            </a:bgClr>
+          </a:pattFill>
         </p:spPr>
         <p:style>
           <a:lnRef idx="2">

2. No transparency option is available in the GUI.

6. Background Fill

1. Start from before.pptx, change fill to Background Fill, resulting to bkgFillOrig.pptx:

--- before/ppt/slides/slide1.xml

+++ bkgFillOrig/ppt/slides/slide1.xml

@@ -19,7 +19,7 @@

           <a:chExt cx="0" cy="0"/>
         </a:xfrm>
       </p:grpSpPr>
-      <p:sp>
+      <p:sp useBgFill="1">
         <p:nvSpPr>
           <p:cNvPr id="4" name="Rectangle 3">
             <a:extLst>

2. No transparency option is available in the GUI.