lab2-1-solution.py

from OpenGL.GL import *
import numpy as np
from glslprogram import fromSource
from app import run

vsCode = """
in vec3 position;
void main()
{
  gl_Position = vec4(position, 1.0);
}
"""

fsCode = """
out vec4 fragColor;
void main()
{
  fragColor = vec4(1.0, 0.0, 1.0, 1.0);
}
"""


def init():

    # create a vertex array object to hold
    vao = glGenVertexArrays(1)
    glBindVertexArray(vao)

    # The actual vertex position data
    # three vertices with three components each: x, y and z
    positions = [
        0.0, 0.8, 0.0,
        0.8, -0.8, 0.0,
        -0.8, -0.8, 0.0
    ]

    # Create and bind an opengl buffer for the position data
    vertexData = glGenBuffers(1)
    glBindBuffer(GL_ARRAY_BUFFER, vertexData)

    # Fill the currently bound buffer with the data, using np to make the data compatible with opengl
    glBufferData(GL_ARRAY_BUFFER, np.array(
        positions, dtype=np.float32), GL_STATIC_DRAW)

    # Compile, link and activate a glsl program defined by the provided vertex- and fragment-shader source code
    program = fromSource(vsCode, fsCode)
    glUseProgram(program)

    # Queries the glsl-program for the location where it will look for data for the "in vec3 position" variable
    posLoc = glGetAttribLocation(program, "position")

    # Ties the currently bound buffer object ("vertexData" above) to the location for the "position" variable. Also describes how the data is layed out in the buffer
    glVertexAttribPointer(posLoc, 3, GL_FLOAT, False, 0, None)

    # Tells opengl to actually use the data tied to the specific location
    glEnableVertexAttribArray(posLoc)

    count = 3
    # Run pipeline using the data and glsl-program that we've provided above
    # Tell it to render triangles, and that we want it to process count (3) vertices
    # This call inplies explicit encoding. So, if we want to render multiple triangles, we have to provide data for 3 extra vertices for each extra triangle
    glDrawArrays(GL_TRIANGLES, 0, count)


run('2DT904 - Providing vertex data', init)