Drawing Lines

[zbych]

I was searching how to draw lines in jPCT but didn't found any good solution that's why I want to present my code and ask: what are possible problems with this solution? I am suspecting that when object/triangle leave camera sight the lines might disappear. Will it cause other problems and how to prevent them?

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public class SimpleLineManager {

public class LineSegmentContainer {
public int segmentLen;
public FloatBuffer segmentBuffer;
public SimpleVector segmentColor;
}

static final int COORDS_PER_VERTEX = 3;
private final int VERTEX_STRIDE = COORDS_PER_VERTEX * 4; // 4 bytes per member

private ArrayList<LineSegmentContainer> _lineSegments;
private GLSLShader _lineShader;
private Object3D _root;
private IRenderHook _renderHook = new IRenderHook() {
@Override
public void setTransparency(float arg0) {}
@Override
public void setCurrentShader(GLSLShader arg0) {}
@Override
public void setCurrentObject3D(Object3D arg0) {}
@Override
public boolean repeatRendering() {
return false;
}
@Override
public void onDispose() {}
@Override
public void beforeRendering(int arg0) {
drawLines();
}
@Override
public void afterRendering(int arg0) {}
};

public SimpleLineManager(GLSLShader lineShader) {
_lineSegments = new ArrayList<SimpleLineManager.LineSegmentContainer>();
_lineShader = lineShader;

float[] vertices = { 0,0,0, -0.0001f,0,0, 0.0001f,0,0};
float[] uvs = { 0,0, 1,1, 1,0};
int[] indices = {0,1,2};

_root = new Object3D(vertices, uvs, indices, 0);
_root.setShader(_lineShader);
_root.setRenderHook(_renderHook);
}

public void addToWorld(World w) {
w.addObject(_root);
}

private void drawLines() {
GLES20.glLineWidth(10f);
int verticesHandle = GLES20.glGetAttribLocation(_lineShader.getProgram(), "position");
int lineColorHandle = GLES20.glGetUniformLocation(_lineShader.getProgram(), "lineColor");
GLES20.glEnableVertexAttribArray(verticesHandle);
for(LineSegmentContainer ls : _lineSegments) {
GLES20.glUniform3f(lineColorHandle, ls.segmentColor.x, ls.segmentColor.y, ls.segmentColor.z);
GLES20.glVertexAttribPointer(verticesHandle, COORDS_PER_VERTEX, GLES20.GL_FLOAT, false, VERTEX_STRIDE, ls.segmentBuffer);
GLES20.glDrawArrays(GLES20.GL_LINE_STRIP, 0, ls.segmentLen);
}
GLES20.glDisableVertexAttribArray(verticesHandle);
}

public void addLineSegment(float[] coords, SimpleVector color) {
ByteBuffer bb = ByteBuffer.allocateDirect(coords.length * 4);
bb.order(ByteOrder.nativeOrder());
FloatBuffer vertexBuffer = bb.asFloatBuffer();
vertexBuffer.put(coords);
vertexBuffer.position(0);
LineSegmentContainer lsc = new LineSegmentContainer();
lsc.segmentBuffer = vertexBuffer;
lsc.segmentColor = color;
lsc.segmentLen = coords.length/3;
_lineSegments.add(lsc);
}

public Object3D getRoot() {
return _root;
}
}


vertex shader

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precision mediump float;

uniform mat4 modelViewProjectionMatrix;
attribute vec4 position;
//attribute vec3 normal;
varying vec4 varVertexColor;

void main(void) {
gl_Position = modelViewProjectionMatrix * position;
}


fragment shader

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precision mediump float;

uniform vec3 lineColor;
uniform float alpha;

void main (void)
{
vec4 base = vec4(lineColor.xyz,alpha);//varVertexColor ;
gl_FragColor = base;
}


[EgonOlsen]

As long as you take care of a clean GL state yourself, i don't see much problems. The thing with line drawing in GL ES is simply that it sucks, because you need different geometry for filled polygons and lines or it will look like crap for anything but the simplest meshes. Using Polylines instead is no option?