How to debug a GLException in Processing? - opengl

Question

I am trying to implement a project related to projection mapping on processing using a custom projection matrix. I found an example that might give me a clue but it is too old and openGL and Processing change a lot meanwhile. I am not very familiar with shaders and openGL, but so far I could update the old code to the version I show below, so you can also compare with the original.
I am still getting a:
GLException: not a gl2 implementation
I am also a bit confused using PGL, GL, PG2 at same time. I feel this is not a good practice.
Original version of the code from Processing 1.0 forum is here.
This is the code I tried to update so far:
import com.jogamp.opengl.*;
import java.nio.FloatBuffer;
float[] modelview = {
0.670984f, 0.250691f, 0.674993f, 0, -0.288247f,
0.966749f, -0.137371f, 0f, -0.68315f, -0.0505059f, 0.720934f, 0f,
0.164808f, 2.1425f, 32.9616f, 1f };
float[] proj = {
0.78125f, 0, 0, 0, 0, 1.04167f, 0, 0, 0, 0, -1.0002f, -1, 0,
0, -2.0002f, 0 };
FloatBuffer mvbuf;
FloatBuffer projbuf;
void setup() {
size(1024, 768, P3D);
PJOGL.profile = 2; //not sure if needed
mvbuf = FloatBuffer.wrap(modelview);
projbuf= FloatBuffer.wrap(proj);
GLProfile glp = GLProfile.get(GLProfile.GL2);
GLCapabilitiesImmutable glcaps = (GLCapabilitiesImmutable) new GLCapabilities(glp);
GLCapabilities tGLCapabilities = new GLCapabilities(glp);
println("System Capabilities:" + glcaps.toString());
println("Profile Details: " + glp.toString());
println("Is GL2 Supported?: " + glp.isGL2());
}
void draw() {
background(0);
PGL pgl = (PJOGL) beginPGL();
GL gl = ((PJOGL) pgl).gl;
GL2 gl2 = gl.getGL2(); //GLException: not a GL2 implemantation
gl2.glMatrixMode(GL2.GL_PROJECTION);
gl2.glLoadIdentity();
gl2.glLoadMatrixf(projbuf);
gl2.glMatrixMode(GL2.GL_MODELVIEW);
gl2.glLoadIdentity();
gl2.glLoadMatrixf(mvbuf);
drawGrid(100, 10, gl2);
endPGL(); //not sure if this is closing what it supposed to
}
void drawGrid(float len, float offset, GL2 g) {
int nr_lines = (int)(len/offset);
g.glColor3f(1, 1, 1);
g.glBegin(g.GL_LINES);
for (int i=-nr_lines; i<nr_lines; i++) {
g.glVertex3f(i*offset, 0, -nr_lines*offset);
g.glVertex3f(i*offset, 0, nr_lines*offset);
}
for (int i=-nr_lines; i<nr_lines; i++) {
g.glVertex3f(-nr_lines*offset, 0, i*offset);
g.glVertex3f(nr_lines*offset, 0, i*offset);
}
g.glEnd();
}

Answer 1

First try this:
PGraphicsOpenGL pg = (PGraphicsOpenGL)g;
println(pg.OPENGL_VERSION);
What does it output? For me this would output:
4.5.0 NVIDIA 376.51
Thereby calling gl.getGL2() fails because an OpenGL 4.5 core context is not backwards compatible with an OpenGL 2.x context.
If I recall correctly then you do have to use PJOGL.profile and set it to 1, to get a backwards compatible context:
PJOGL.profile = 1;
Note that if you're using Processing 3.0, then you might have to utilize settings():
void settings() {
size(1024, 768, P3D);
PJOGL.profile = 1;
}