Basic support for Transform Feedback #1078

TehLeo · 2019-04-25T12:41:28Z

Adds basic support for Transform Feedback (TF).
As part of discussion on discord

new class BufferObject was added which manages BufferObjects
VertexBuffer now extends BufferObject
jme3.shader.BufferObject was renamed to UniformBufferObject and now extends BufferObject

To support basic transform feedback.

setTransformFeedbackOutput(TransformFeedbackOutput output) method was added to the Renderer interface

The use of this method is similar to how rendering of framebuffers is handled in jme. This method is called to enable transform feedback, after which rendered geometry's TF ouput will be captured to the specified output buffers. Calling it will null, disables transform feedback.

In order to use TF, a shader has to specify the output variables which will be outputted to TF. This is accomplished by specifying the output variables in Technique block of .j3md file. Syntax is:

TransformFeedback [Off | Interleaved | Separate | InShader] varying1 varying2 varying3 ...

For example a vertex/geometry shader contains the ouput:

out mat4 TransformFeedback;

A technique can be written as:

Technique {
    VertexShader GLSL130: jme3test/renderer/TestTR.vert
    GeometryShader GLSL150: jme3test/renderer/TestTR.geom
    RenderState {
        RasterizerDiscard On
    }
    TransformFeedback Interleaved TransformFeedback
}

added Render State RasterizerDiscard - when enabled Fragment Processing stage is skipped,
added QueryObject, retrieve the number of written primitives for TF operation
added TF testcase jme3test.renderer.TestTransformFeedback

Awaiting your feedback.

update

jme3-core/src/main/java/com/jme3/app/DetailedProfiler.java

riccardobl · 2019-10-16T21:08:30Z

jme3-core/src/main/java/com/jme3/material/RenderState.java

@@ -34,6 +34,8 @@
 import com.jme3.export.*;
 import com.jme3.scene.Mesh;
 import java.io.IOException;
+import java.util.Arrays;
+import java.util.Objects;


Unused imports

thank you for pointing them out, i'll fix these with next commit

riccardobl · 2019-10-16T21:11:51Z

jme3-core/src/main/java/com/jme3/renderer/Caps.java

+    public static boolean supports(Collection<Caps> caps, QueryObject query) {
+        switch(query.getType()) {
+            case SamplesPassed:
+                //GL1.5 is available or (GL_ARB_occlusion_query)


So.. are we supposed to test if 1.5 is available?

I am under the impression JME is GL 2.0+ so no need to test?

What about GL ES?

This will have to be investigated, a quick check I made, it seems gl es 2.0 might not support occlusion queries.

riccardobl · 2019-10-16T21:14:06Z

jme3-core/src/main/java/com/jme3/renderer/Renderer.java

 import com.jme3.scene.VertexBuffer;
-import com.jme3.shader.BufferObject;
+import com.jme3.shader.UniformBufferObject;


Unused import

riccardobl · 2019-10-16T21:55:21Z

jme3-core/src/main/java/com/jme3/renderer/RenderContext.java

+    /**
+     * Started queries.
+     */
+    public int[] startedQueries = new int[6/*QueryObject.Type.values().length*/];


What is the point of this? Just to remember which queries where started? Do we really need it?

Yes, unless a query is started issuing a glEndQuery or checking for result yield a glerror. This is here to prevent that. Furthermore, take a look at the following

void glBeginQuery(GLenum target, GLuint id); void glEndQuery( GLenum target);

Do you see something off about the functions above?
The off thing about them is that glEndQuery does not take query id as a parameter!

Thus in other words lets say I make two timer queries:

queryT1 = new QueryObject(app.getRenderer(), QueryObject.Type.TimeElapsed); queryT2 = new QueryObject(app.getRenderer(), QueryObject.Type.TimeElapsed);

If you run the following code:

queryT1.begin(); queryT2.begin(); //some work queryT2.end(); queryT1.end();

You will correctly get a RenderException (at line queryT2.begin();)

com.jme3.renderer.RendererException: Query of type TimeElapsed already started.

Without the render exception you would get gl error. In other words you are not allowed to nest the same type of query.

Sure, but this is never exposed outside of the core. So maybe we don't need those checks ...

Are you saying that users will not be able to use QueryObject? I believe we do need them as otherwise its pretty easy to get gl errors.

As usual there is nothing stopping you from using internals in jme, but imo this is not an end user feature so maybe we can avoid having all those extra checks.

Why not have the checks? Those checks are not expensive. You are not starting 10 thousands of queries per frame. They only bring robustness. So I do not see a reason for them not to be there.
Also even if it was used just in internals, there's always a risk that you can nest some queries and this would be a nightmare for figuring out such error.
Eg. Imagine you use TimerQuery while you also have DetailedProfiler attached. And there you go... nested queries.

riccardobl · 2019-10-16T22:10:36Z

jme3-core/src/main/java/com/jme3/renderer/QueryObject.java

+package com.jme3.renderer;
+
+import com.jme3.util.NativeObject;
+import java.util.EnumMap;


Unused import?

riccardobl · 2019-10-16T22:11:29Z

jme3-core/src/main/java/com/jme3/renderer/QueryObject.java

+         */
+        CanEnd
+    }
+


Is this really needed?

Refer to the answer above, in short, to prevent gl errors.

leo and others added 10 commits April 19, 2019 14:41

refactor base class buffer object

0037e13

refactor base class buffer object2

13b7fe8

transform feedback, query object, rast discard

74eee97

doc, edit

b5f4884

doc, rast disc edit

0982529

update

17e1787

Merge branch 'jMonkeyEngine-master' into rBasicTF

6d2c007

update

update 2

6d0142e

update 3

98dd9d2

update 4

24056d6

riccardobl reviewed Oct 16, 2019

View reviewed changes

Merge branch 'master' into rBasicTF

1cace5e

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Basic support for Transform Feedback #1078

Basic support for Transform Feedback #1078

TehLeo commented Apr 25, 2019

riccardobl Oct 16, 2019

TehLeo Oct 17, 2019 •

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Basic support for Transform Feedback #1078

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Basic support for Transform Feedback #1078

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TehLeo commented Apr 25, 2019

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TehLeo Oct 17, 2019 •

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