Qt3D. Draw Transparent Qspheremesh Over Triangles

Qt3d. Draw transparent QSphereMesh over triangles

My mistake was that i did wrong order of creating and deletion of Triangles and Sphere entities.

In pseudo code right order is as follows:

clearTriangles();
clearSphere();       
drawTriangles();
drawSphere();

Draw triangle with Qt3D

Your points are set in clockwise order you can reorder them or set a different behaviour via this link: doc.qt.io/qt-5.11/qt3drender-qcullface.html

If you need both i would give a try to Qt3DRender::QCullFace::NoCulling

Draw transparent image over the screen with Qt

I have tried your code and it works fine, apparently it seems to be a problem of the image, I recommend you to use some kind of external application to erase the transparent parts like this.

Here is a test that works with your code:

If you want to do this automatically I recommend you to use opencv.

GeometryRenderer Why render lines, but not Triangles

If I adapt your QML the following way then I can see two triangles:

import QtQuick 2.2
import Qt3D.Core 2.0
import Qt3D.Render 2.0
import Qt3D.Extras 2.0

Entity {
    id: root
    PhongMaterial { id: material; diffuse: Qt.rgba(0.8, 0., 0., 1.0) }
    GeometryRenderer {
        id: renderer
        primitiveType: GeometryRenderer.Triangles
        instanceCount: 1
        geometry: Geometry {
            Attribute {
                name: defaultPositionAttributeName
                attributeType: Attribute.VertexAttribute
                vertexBaseType: Attribute.Float
                vertexSize: 3
                byteOffset: 0
                byteStride: 3 * 4
                count: 6
                buffer: Buffer {
                    type: Buffer.VertexBuffer
                    data: new Float32Array([
                                    // #1 triangle
                                    -0.9, -0.5, 0.0,
                                    -0.0, -0.5, 0.0,
                                    -0.45, 0.5, 0.0,
                                    // #2 triangle
                                    0.0, -0.5, 0.0,
                                    0.9, -0.5, 0.0,
                                    0.45, 0.5, 0.0,
                                ])
                }
            }
        }
    }
    components: [ renderer, material ]
}

I suppose the error is related to the wrong hierarchy of GeometryRenderer and Entity.

To get correct lighting you need to give the GeometryRenderer the vertexNormals too.

Edit:

As it is a common question whether a GeometryRenderer always needs an indexBuffer for primitiveType: Triangles, TriangleStrip, and TriangleFan, I'll come up with a somewhat more detailed answer.

A GeometryRenderer of primitiveType: Triangles does not necessarily need an index array (I checked the source code of Qt3D as I was unsure).

The reason you are not seeing your triangles is: You are defining the vertices in the wrong order! Change the order of the vertices in the vertexBuffer so that every three consecutive vertices form a triangle when going counterclockwise around the triangle. The triangle normal will then point at you.

Or, have a look onto your Entity from the opposite direction: you'll see the two triangles.

When using huge buffers and you don't want to repeat large amounts of vertices for memory/efficiency reasons you'll definitely should consider using an indexBuffer.

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