Debug Rendering (Beginner) [Solved]

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Debug Rendering (Beginner) [Solved]

Postby rystills » Wed Jun 12, 2019 2:14 pm

Hi,
I've recently switched my game engine from using Bullet Physics to using Newton Dynamics, but I'm having a little trouble converting everything to Newton. I suspect the core issue stems from how I'm syncing rotations between my engine (in which I store rotations in glm 4x4 matrices) and my NewtonBodies, but rather than trouble you with my own bugs, I'd like to get debug rendering operational so I can see for myself what's happening. What is the simplest way to go about debug rendering Newton Dynamics in OpenGL? Ideally I would like to be able to iterate over NewtonCollision shape triangles so that I can render them as a wireframe during my engine's post-render stage. I recall reading about a callback that might allow me to do just that, but I don't quite know how to use it.
Last edited by rystills on Thu Jun 13, 2019 12:28 am, edited 2 times in total.
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Re: Debug Rendering (Beginner)

Postby Julio Jerez » Wed Jun 12, 2019 2:40 pm

if you doaloaded the SDK there is a file tha constain many unility function tat do that.

void DebugRenderWorldCollision (const NewtonWorld* const world, DEBUG_DRAW_MODE mode);

will iterate over the world, qeuering each body and form each body each collision shape and converting them to glBegin(GL_LINES);
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Re: Debug Rendering (Beginner)

Postby Sweenie » Wed Jun 12, 2019 2:49 pm

The function NewtonCollisionForEachPolygonDo is what you need to use.
Mind though that the callback can return a 4-sided polygon for some collision shapes, not just triangles.
But you could just split the 4-sided one in two if you only want triangles i suppose.

http://www.newtondynamics.com/wiki/inde ... hPolygonDo
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Re: Debug Rendering (Beginner)

Postby Julio Jerez » Wed Jun 12, 2019 3:27 pm

Sweenie wrote:Mind though that the callback can return a 4-sided polygon for some collision shapes, not just triangles.

an n sided, but is a convex so is easy to fan it
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Re: Debug Rendering (Beginner)

Postby rystills » Wed Jun 12, 2019 5:25 pm

Brilliant, thank you both!

NewtonCollisionForEachPolygonDo, along with the NewtonCollisionIterator callback, made it quick and easy to render some debug wireframes. As a result, I have spotted some rotation errors and am working to resolve them, however I will elucidate the nature of those errors in a separate thread if necessary.

For future reference, below is the code that I used to achieve debug rendering. The newton debug render callback was copied from newton_dynamics\applications\demosSandbox\sdkDemos\toolBox\DebugDisplay.cpp -> DebugShowGeometryCollision, and the line render method I think is adapted from an old forum post explaining debug rendering in Bullet Physics (though of course, it is just as useful with Newton).

Code: Select all
void debugDrawLine(const glm::vec3& from, const glm::vec3 &to, const glm::vec3& color) {
   // Vertex data
   GLfloat points[12];

   points[0] = from.x;
   points[1] = from.y;
   points[2] = from.z;
   points[3] = color.x;
   points[4] = color.y;
   points[5] = color.z;

   points[6] = to.x;
   points[7] = to.y;
   points[8] = to.z;
   points[9] = color.x;
   points[10] = color.y;
   points[11] = color.z;

   glDeleteBuffers(1, &VBO);
   glDeleteVertexArrays(1, &VAO);
   glGenBuffers(1, &VBO);
   glGenVertexArrays(1, &VAO);
   glBindVertexArray(VAO);
   glBindBuffer(GL_ARRAY_BUFFER, VBO);
   glBufferData(GL_ARRAY_BUFFER, sizeof(points), &points, GL_STATIC_DRAW);
   glEnableVertexAttribArray(0);
   glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), 0);
   glEnableVertexAttribArray(1);
   glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat)));
   glBindVertexArray(0);

   glBindVertexArray(VAO);
   glDrawArrays(GL_LINES, 0, 2);
   glBindVertexArray(0);
}

void debugDrawNewtonCallback(void* const userData, int vertexCount, const dFloat* const faceVertec, int faceId) {
   int index = vertexCount - 1;
   dVector p0(faceVertec[index * 3 + 0], faceVertec[index * 3 + 1], faceVertec[index * 3 + 2]);
   for (int i = 0; i < vertexCount; i++) {
      dVector p1(faceVertec[i * 3 + 0], faceVertec[i * 3 + 1], faceVertec[i * 3 + 2]);
      debugDrawLine(glm::vec3(GLfloat(p0.m_x), GLfloat(p0.m_y), GLfloat(p0.m_z)), glm::vec3(GLfloat(p1.m_x), GLfloat(p1.m_y), GLfloat(p1.m_z)), glm::vec3(255, 255, 255));
      p0 = p1;
   }
}

void debugDrawNewton() {
   for (int i = 0; i < gameObjects.size(); ++i) {
      dMatrix tm;
      NewtonBodyGetMatrix(gameObjects[i]->body, &tm[0][0]);
      NewtonCollisionForEachPolygonDo(NewtonBodyGetCollision(gameObjects[i]->body), &tm[0][0], debugDrawNewtonCallback, NULL);
   }
}
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