[Soc-2017-dev] vertex paint project - ply exporter

Howard Trickey howard.trickey at gmail.com
Mon Jul 24 15:30:50 CEST 2017 

Hi Darshan,

I will have to look more about baking to see if there is another way, but
glad you found one way.

Interesting about the backface culling. I was suspecting that the artifacts
we were seeing were due to backfaces. But as you say, culling them is not
really the best fix here. Still, a good clue.

As discussed in IRC, I did the steps to the Builder to build your branch.
It seemed to work.  Some builds are building now. For the record, here's
what I did
git checkout experimental-build
git merge master
git merge --squash soc-2017-vertex_paint
git commit -a
git revert HEAD

noted that commit for the place where your code is merged in is: de3ee9f7bb



On Sun, Jul 23, 2017 at 11:08 AM Darshan kadu <darsh7807 at gmail.com> wrote:

> Hello, Mr, Howard,
>
> I had a hard time in understanding how does the bake to vertex color
> works, but I figured it out.
>
> I did the following steps:
> 1) I set the texture are the random image.
> 2)Set the UV map
> 3)in the physics tab get to dynamic paint tab
> 4)Add canvas
> 5)dynamic output: add paintmap later
> 6)dynamic initial color:
>    initial color: UV texture
>  and then set the texture
> 7) go to object modifier tab
>    click apply.
>
> If we subdivide sufficiently we can see the image in vertex paint.
> Here alpha is by default 1.
> I followed these instructions:
> https://blender.stackexchange.com/questions/26503/how-to-bake-uv-map-texture-to-vertex-color-selected-to-active/41677
>
>
> I just want to know whether is this the correct way to bake or any other
> method is there to bake?
> This was only for texture to vertex color baking.
>
> Well, I enabled the backface culling in the shading panel on the
> right-hand side, the alpha for subdivide was showing properly. But it
> doesn't consider the back faces and for things like a plane, it's not
> good(as the one side in invisible).
> We can set it as default by GL functions, but it won't be correct, right?
>
> Thank you.
>
>
> On Sat, Jul 22, 2017 at 5:36 PM, Howard Trickey <howard.trickey at gmail.com>
> wrote:
>
>> Hi Darshan,
>>
>> The channel locks seem to work. Thanks.
>>
>> I think bake color is a great next step.
>>
>> On Sat, Jul 22, 2017 at 7:03 AM Darshan kadu <darsh7807 at gmail.com> wrote:
>>
>>> Hello, Mr. Howard,
>>>
>>> I have implemented the color lock and the alpha blend, have a look at it
>>> I have pushed the code.
>>>
>>> I am now planning to work on bake color. What do you think?
>>>
>>> Thank you.
>>>
>>> On Thu, Jul 20, 2017 at 6:15 PM, Howard Trickey <
>>> howard.trickey at gmail.com> wrote:
>>>
>>>> Hi Darshan,
>>>>
>>>> Your plan to next work blending alpha according to mode, and locking
>>>> color, seems good to me.
>>>>
>>>> Somehow I don't think depth ordering is the issue with the transparent
>>>> display.  We'll have to leave this as a background task to fix while moving
>>>> on to other things now.  This is only meant at the moment as a kind of
>>>> quick hack so the user can see some effect of changing alpha in Vertex
>>>> Paint mode, and that much is accomplished.
>>>>
>>>> The concept of padding is that each C data type takes a certain number
>>>> of bytes and is (by default, and by most compilers) aligned on certain
>>>> "address boundaries" because machines access them better that way. On
>>>> typical machines today:
>>>> char, bool - take 1 byte, can go at any address
>>>> short - takes 2 bytes, goes on even addresses
>>>> int, long, float, pointer - take 4 bytes, go on multiple-of-4 addresses
>>>> double - takes 8 bytes, goes on multiple-of-8 addresses
>>>>
>>>> So when you declare a struct, it puts them in order but if the next
>>>> address available would not fit the above rules, internal padding
>>>> (basically, unused bytes) is inserted in order to make the required
>>>> alignment. For more information, read, say
>>>> https://en.wikipedia.org/wiki/Data_structure_alignment
>>>>
>>>> With some structs in Blender that are to be persisted to disk, we want
>>>> the total length of the struct to have size that is a multiple of 8. If by
>>>> following the above rules, you end up with a struct that is not a multiple
>>>> of 8, you may have to add declaration of some chars and possibly an int in
>>>> order to end up with a multiple of 8. Also, it seems that we explicitly put
>>>> in pad declarations rather than relying on the compiler to do it for
>>>> 'jumps' caused by alignment concerns. I guess this is to make it easy for a
>>>> program to do size calculations when looking at the struct defs in the
>>>> makesdna directory.  E.g., see the ID and PreviewImage struct defs in
>>>> makesdna/DNA_ID.h for both types of pads.
>>>>
>>>> On Thu, Jul 20, 2017 at 6:07 AM Darshan kadu <darsh7807 at gmail.com>
>>>> wrote:
>>>>
>>>>> Hello, Mr. Howard,
>>>>>
>>>>> Yes, I also think that the alpha should be blend similar to rgb. It
>>>>> will be simple to implement.
>>>>>
>>>>> About the channel lock, the artists want it, so having it would be
>>>>> good think, I can do it with r,g,b bool in the brush struct and changing
>>>>> them from  UI,  Can you tell me the concept of padding you mention before
>>>>> for adding element in the structure.
>>>>>
>>>>> For visualization section, Can cull face be useful? but for the cases
>>>>> like plane the back view will not be displayed.
>>>>>
>>>>> Another thing that can be done is drawing according the depth the most
>>>>> depth faces first, I haven't done it before). This blog explains this very
>>>>> well https://learnopengl.com/#!Advanced-OpenGL/Blending.
>>>>>
>>>>> But again why only some faces are behaving like that, why not all?
>>>>> This is something interesting!
>>>>>
>>>>> Now, I will be adding the alpha blending similar to rgb, and locking
>>>>> color.
>>>>>
>>>>> Thank you.
>>>>>
>>>>> On Wed, Jul 19, 2017 at 7:39 PM, Darshan kadu <darsh7807 at gmail.com>
>>>>> wrote:
>>>>>
>>>>>> Hello, Mr. Howard,
>>>>>> Sorry, I was ill from yesterday afternoon. I should haven't told you
>>>>>> before but internet wasn't very good its monsoon season(heàvy rain) in
>>>>>> India.
>>>>>>
>>>>>> Meanwhile, yesterday I changed the ply importer to take alpha into
>>>>>> account. I have pushed the code. I thing the same problem comes with the
>>>>>> fbx importer. I will check it. I will give reply to your mail as soon as
>>>>>> possible.
>>>>>>
>>>>>> Sorry, I should have told you yesterday itself.
>>>>>>
>>>>>> Thank you.
>>>>>>
>>>>>> On 19-Jul-2017 6:40 PM, "Howard Trickey" <howard.trickey at gmail.com>
>>>>>> wrote:
>>>>>>
>>>>>>> Darshan,
>>>>>>>
>>>>>>> What are you working on now?
>>>>>>>
>>>>>>> I looked a little more at the issue of alpha display after
>>>>>>> subdividing. I am pretty sure now that the alphas are set properly -- if
>>>>>>> you remove all but, say, the front (subdivided) face, the display looks OK.
>>>>>>> I tried changing the glBlendfunc call to:
>>>>>>> glBlendFuncSeparate(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA, GL_ONE,
>>>>>>> GL_ONE_MINUS_SRC_ALPHA);
>>>>>>> which seems more correct, but it didn't make any difference.
>>>>>>>
>>>>>>> Maybe someone reading this with more experience with OpenGL and
>>>>>>> alpha-blending has an idea?  I wonder if somehow we have to turn on drawing
>>>>>>> the elements in proper z-sorted order?
>>>>>>>
>>>>>>>
>>>>>>> On Tue, Jul 18, 2017 at 9:48 AM Howard Trickey <
>>>>>>> howard.trickey at gmail.com> wrote:
>>>>>>>
>>>>>>>> Darshan,
>>>>>>>>
>>>>>>>> I made a little python function to dump the vertex (loop) colors on
>>>>>>>> the console.  You may find this useful.  If you put this in, say, the
>>>>>>>> release/scripts/startup folder then you can use the <Space>-menu to search
>>>>>>>> for 'Dump Vertex Colors'.  To see which faces and vertices correspond to
>>>>>>>> which dumped colors, you can start blender with --debug and then enable the
>>>>>>>> 'indices' visualization box in the right-hand panel of view3d (when in Edit
>>>>>>>> mode) to see the indices of the currently selected elements.
>>>>>>>>
>>>>>>>> I think there may be a problem with the ply exporter, discovered by
>>>>>>>> using this. I made a simple plane quad and put different colors and alphas
>>>>>>>> on each, and then the ply exporter seemed to have an off-by-one error in
>>>>>>>> lining up colors with vertices. But I looked briefly at the code and didn't
>>>>>>>> see what was wrong.
>>>>>>>>
>>>>>>>> I also checked the interpolation of alpha's when subdividing and
>>>>>>>> agree with you that it seems to be doing approximately the right thing, so
>>>>>>>> the problem is somehow in the visualization code.
>>>>>>>>
>>>>>>>
>>>>>>> _______________________________________________
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>>>>>>> Soc-2017-dev at blender.org
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>>>>>>>
>>>>>>>
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>>>>
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