How to draw a mesh with GLGraphics

eskimoblo..

How to draw a mesh with GLGraphics

in Contributed Library Questions • 2 years ago

I want to draw a simple rectangle mesh with GLGraphics where I can change the vertices in the shader later on :

ArrayList<PVector> vertices = new ArrayList<PVector>();
int size = audio.getPeakSize();

for (int i = 0; i <= size; i++) {
float x = 1.0f / size * i;
for (int j = 0; j <= size; j++) {
float y = 1.0f / size * j;
vertices.add(new PVector(x, y));
}
}
model = new GLModel(this, vertices.size(), QUAD_STRIP, GLModel.STATIC);
model.updateVertices(vertices);

But this doesn't draw a real mesh. In my understanding I have to add the indicies so that OPENGL knows howto build the strip. Does anyone knows how to get this work?

Replies(2)

eskimoblo..

Re: How to draw a mesh with GLGraphics

2 years ago

So after reading the MillionCubes example I came up with this but it gives me a "Wrong number of indices!" error

private void initRaster() {
ArrayList<PVector> vertices = new ArrayList<PVector>();
ArrayList<Integer> indices = new ArrayList<Integer>();
float numU = 1, numV = 1;
float cnt = numU / audio.getPeakSize();
int size = audio.getPeakSize();
size = 5;
for (int i = 0; i <= size; i++) {
for (int j = 0; j <= size; j++) {
float x = 1.0f / size * i;
float y = 1.0f / size * j;
vertices.add(new PVector(x, y));
if(i<size && j<size){
int s = size +1;
int p1 = i*s + j;
int p2 = (i+1)*s + j;
int p3 = i*s + j +1;
int p4 = (i+1)*s + j + 1;
indices.add(p1);
indices.add(p2);
indices.add(p3);
indices.add(p2);
indices.add(p4);
indices.add(p3);
println(p1 + " " + p2 + " " +p3);
println(p2 + " " + p4 + " " +p3);
}
}
}
println(vertices.size());
int[] in = new int[indices.size()];
for (int i=0; i<indices.size(); i++){
in[i]=indices.get(i);
}
model = new GLModel(this, vertices, TRIANGLE_STRIP, GLModel.STATIC);
model.updateIndices(in);
}

eskimoblo..

Re: How to draw a mesh with GLGraphics

2 years ago

Ok I've got it. I've to initIndices before adding them. Also using TRIANGLE_STRIP isn't a good idea, just using TRIANGLES solves the last bug:

private void initRaster() {
ArrayList<PVector> vertices = new ArrayList<PVector>();
ArrayList<Integer> indices = new ArrayList<Integer>();
int size = audio.getPeakSize();
for (int i = 0; i <= size; i++) {
for (int j = 0; j <= size; j++) {
float x = 1.0f / size * i;
float y = 1.0f / size * j;
vertices.add(new PVector(x, y));
if(i<size && j<size){
int s = size +1;
int p1 = i*s + j;
int p2 = (i+1)*s + j;
int p3 = i*s + j +1;
int p4 = (i+1)*s + j + 1;
indices.add(p1);
indices.add(p2);
indices.add(p3);
indices.add(p2);
indices.add(p4);
indices.add(p3);
}
}
}
int[] in = new int[indices.size()];
for (int i=0; i<indices.size(); i++){
in[i]=indices.get(i);
}
model = new GLModel(this, vertices, TRIANGLES, GLModel.STATIC);
model.initIndices(in.length);
model.updateIndices(in);
}

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