Develop Reference

Moving a point using cordinate in 2D OpenGL Python

Suppose I have a point in pixel (200,200), and I would like to just shift it to (400,400) pixel. Is there any way to do it without glClear() as I don't want my other objects to get erased?
Here is the code that I am using for drawing a single point:
from OpenGL.GL import *
from OpenGL.GLUT import *
from OpenGL.GLU import *
def draw_points(x0,y0):
glPointSize(5)
glBegin(GL_POINTS)
glVertex2f(x0,y0)
glEnd()
def iterate():
glViewport(0, 0, 1000, 1000)
glMatrixMode(GL_PROJECTION)
glLoadIdentity()
glOrtho(0.0, 1000, 0.0, 1000, 0.0, 1.0)
glMatrixMode (GL_MODELVIEW)
glLoadIdentity()
def showScreen():
elapesed_ms = glutGet(GLUT_ELAPSED_TIME)
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
glLoadIdentity()
iterate()
glColor3f(255, 255, 255)
draw_points(200,200)
glutSwapBuffers()
glutInit()
glutInitDisplayMode(GLUT_RGBA)
glutInitWindowSize(1000, 1000)
glutInitWindowPosition(0, 0)
wind = glutCreateWindow(b"")
glutDisplayFunc(showScreen)
glutMainLoop()

PyOpenGL not drawing anything after clearing

I used Glut for making window and wanted to draw triangle, then on click button redraw it, but after clearing window I can't draw again. Does something wrong with Buffer depth and buffer bit? If I cleared it do I need to setup both again in my draw function?
def drawSomething():
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
glLoadIdentity()
glTranslatef(-2.5, 0.5, -6.0)
glColor3f( 1.0, 1.5, 0.0 )
glPolygonMode(GL_FRONT, GL_FILL)
glBegin(GL_TRIANGLES)
glVertex3f(2.0,-1.2,0.0)
glVertex3f(2.6,0.0,0.0)
glVertex3f(2.9,-1.2,0.0)
glEnd()
glFlush()
def funcForUpdate():
glClearColor(0.0, 0.0, 0.0, 0)
glClear(GL_COLOR_BUFFER_BIT)
glEnable(GL_TEXTURE_2D)
glBegin(GL_QUADS)
glTexCoord2f(0.0, 0.0)
glVertex2f(0.0, 0.0)
glTexCoord2f(0.0, 1.0)
glVertex2f(0.0, width)
glTexCoord2f(1.0, 1.0)
glVertex2f(height, width)
glTexCoord2f(1.0, 0.0)
glVertex2f(height, 0.0)
glEnd()
glFlush()
def resizeUpdateFunc(width, height):
glMatrixMode(GL_MODELVIEW)
glLoadIdentity()
gluOrtho2D(0.0, width, 0.0, height)
def handleKey(bkey,x,y):
key = bkey.decode("utf-8")
if key == "a":
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
drawSomething()
glFlush()
glutInit()
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB)
glutInitWindowSize(width, height)
glutInitWindowPosition(0, 0)
glutCreateWindow("test")
drawSomething()
glutDisplayFunc(funcForUpdate)
glutReshapeFunc(resizeUpdateFunc)
glutKeyboardFunc(handleKey)
glutMainLoop()

See glutDisplayFunc:
[...] sets the display callback for the current window. [...] The redisplay state for a window can be either set explicitly by calling glutPostRedisplay or implicitly as the result of window damage reported by the window system.
In fact, a triangle is drawn in drawSomething, but it is immediately overdrawn in funcForUpdate.
Add a state drawTriangle and set the state in handleKey:
drawTriangle = False
def handleKey(bkey, x, y):
global drawTriangle
key = bkey.decode("utf-8")
if key == "a":
drawTriangle = not drawTriangle
glutPostRedisplay()
Draw depending on the variable drawTriangle in funcForUpdate:
def funcForUpdate():
glClearColor(0, 0, 0, 0)
glClear(GL_COLOR_BUFFER_BIT)
# [...]
if drawTriangle:
# [...]
glFlush()
A complete example:
from OpenGL.GL import *
from OpenGL.GLU import *
from OpenGL.GLUT import *
drawTriangle = False
def funcForUpdate():
glClearColor(0, 0, 0, 0)
glClear(GL_COLOR_BUFFER_BIT)
glColor3f(1, 1, 0)
glBegin(GL_QUADS)
glVertex2f(0.0, 0.0)
glVertex2f(0, height)
glVertex2f(width, height)
glVertex2f(width, 0)
glEnd()
if drawTriangle:
glPushMatrix()
glLoadIdentity()
glTranslate(width/2, height/2, 0)
glColor3f(1, 0, 0)
glBegin(GL_TRIANGLES)
glVertex3f(-width/4, -height/4, 0)
glVertex3f(width/4, -height/4, 0)
glVertex3f(width/4, height/4, 0)
glEnd()
glPopMatrix()
glFlush()
def resizeUpdateFunc(width, height):
glMatrixMode(GL_PROJECTION)
glLoadIdentity()
gluOrtho2D(0.0, width, 0.0, height)
glMatrixMode(GL_MODELVIEW)
glLoadIdentity()
def handleKey(bkey, x, y):
global drawTriangle
key = bkey.decode("utf-8")
if key == "a":
drawTriangle = not drawTriangle
glutPostRedisplay()
width, height = 320, 200
glutInit()
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB)
glutInitWindowSize(width, height)
glutInitWindowPosition(0, 0)
glutCreateWindow("test")
glutDisplayFunc(funcForUpdate)
glutReshapeFunc(resizeUpdateFunc)
glutKeyboardFunc(handleKey)
glutMainLoop()

Pyglet draw text into texture

I'm trying to render an image with OpenGL using Pyglet. So far I've been able to setup the framebuffer and texture, render into it and save it as a PNG image. But I can't find out how to use Pyglets font rendering.
import numpy as np
import pyglet
from pyglet.gl import *
from ctypes import byref, sizeof, POINTER
width = 800
height = 600
cpp = 4
# Create the framebuffer (rendering target).
buf = gl.GLuint(0)
glGenFramebuffers(1, byref(buf))
glBindFramebuffer(GL_FRAMEBUFFER, buf)
# Create the texture (internal pixel data for the framebuffer).
tex = gl.GLuint(0)
glGenTextures(1, byref(tex))
glBindTexture(GL_TEXTURE_2D, tex)
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_FLOAT, None)
# Bind the texture to the framebuffer.
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, tex, 0)
# Something may have gone wrong during the process, depending on the
# capabilities of the GPU.
res = glCheckFramebufferStatus(GL_FRAMEBUFFER)
if res != GL_FRAMEBUFFER_COMPLETE:
raise RuntimeError('Framebuffer not completed')
glViewport(0, 0, width, height)
# DRAW BEGIN
# =====================
glClearColor(0.1, 0.1, 0.1, 1.0)
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glColor3f(1.0, 0.5, 0.02)
glRectf(-0.75, -0.75, 0.75, 0.75)
glColor3f(1.0, 1.0, 1.0)
label = pyglet.text.Label(
"Hello, World", font_name='Times New Roman', font_size=36,
x=0, y=0, anchor_x='center', anchor_y='center')
label.draw()
# =====================
# DRAW END
# Read the buffer contents into a numpy array.
data = np.empty((height, width, cpp), dtype=np.float32)
glReadPixels(0, 0, width, height, GL_RGBA, GL_FLOAT, data.ctypes.data_as(POINTER(GLfloat)))
# Save the image.
import imageio
data = np.uint8(data * 255)
imageio.imwrite("foo.png", data)
The text does not appear on the framebuffer. How can I render the label on the framebuffer?

For rendering labels in Pyglet, first, an orthographic projection should be set up. In the given example, do it as follows:
glMatrixMode(GL_PROJECTION)
glLoadIdentity()
glOrtho(0, width, 0, height, -1, 1)
glMatrixMode(GL_MODELVIEW)
glLoadIdentity()
glColor3f(1.0, 1.0, 1.0)
label = pyglet.text.Label(
"Hello, World", font_name='Times New Roman', font_size=36,
x=width/2, y=height/2, anchor_x='center', anchor_y='center')
label.draw()
Then, the label is rendered as expected. (Note: moved the label's offset to the image center, i.e. x=width/2, y=height/2,)
foo.png (output framebuffer image)

PyOpenGL multitexture error - invalid operation

I'm trying to make a game that uses pygame and OpenGL in python 3, but i keep getting the same error:
OpenGL.error.GLError: GLError(
err = 1282,
description = b'invalid operation',
baseOperation = glClear,
cArguments = (16640,)
)
Here is my code:
PART A - Create and Configure
Surface = pygame.display.set_mode((WIDTH, HEIGHT), pygame.OPENGL)
glViewport(0, 0, WIDTH, HEIGHT)
glMatrixMode(GL_PROJECTION)
glLoadIdentity()
gluOrtho2D(-8.0, 8.0, -6.0, 6.0)
glMatrixMode(GL_MODELVIEW)
glLoadIdentity()
glShadeModel(GL_SMOOTH)
glClearColor(0.0, 0.0, 0.0, 0.0)
glClearDepth(1.0)
glDisable(GL_DEPTH_TEST)
glDisable(GL_LIGHTING)
glDepthFunc(GL_LEQUAL)
glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST)
glEnable(GL_BLEND)
PART B - Creating Texture
class Texture():
# simple texture class
# designed for 32 bit png images (with alpha channel)
def __init__(self,fileName):
self.texID=0
self.LoadTexture(fileName)
def LoadTexture(self,fileName):
try:
textureSurface = pygame.image.load(fileName).convert_alpha()
textureData = pygame.image.tostring(textureSurface, "RGBA", True)
self.w, self.h = textureSurface.get_size()
self.texID=glGenTextures(1)
glBindTexture(GL_TEXTURE_2D, self.texID)
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR)
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR)
glTexImage2D( GL_TEXTURE_2D, 0, GL_RGBA, textureSurface.get_width(),
textureSurface.get_height(), 0, GL_RGBA, GL_UNSIGNED_BYTE,
textureData )
except Exception as E:
print(E)
print ("can't open the texture: %s"%(fileName))
def __del__(self):
glDeleteTextures(self.texID)
def get_width(self):
return self.w
def get_height(self):
return self.h
PART C - Prepering the screen
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
glLoadIdentity()
glDisable(GL_LIGHTING)
glEnable(GL_TEXTURE_2D)
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)
PART D - Adding Texture
def blit(texture, x, y):
glPushMatrix()
glTranslatef(x, y, 0.0)
glBindTexture(GL_TEXTURE_2D, texture.texID)
I looked it up, and apparently PyOpenGL 3 has this unfixed bug when try to render more than one texture. I use python 3.3, and dont wanna downgrade to 2.x, and i cant find a OpenGL 2 for python 3. Is there an away around this bug? Am i doing something wrong?

The OpenGL Context is thread local. If you try to invoke an OpenGL statement from another thread without making current the OpenGL context current, you will get an INVALID_OPERATION error.
Unfortunately, PyGame does not offer a function to make the OpenGL context explicitly current.
Another possibility is that you missed closing a glBegin/glEndsequence withglEnd` somewhere.

Multi-texturing in PyOpenGL using a GLSL shader

I would like to be able to combine two textures in a GLSL fragment shader. I am currently using PyOpenGL and everything i've done up to this point using shaders has worked fine.
I am running into difficulty when I try to access multiple textures from the fragment shader, for instance, the following shader displays the correct texture minus the blue pixels:
uniform sampler2D my_texture1;
uniform sampler2D my_texture2;
void main()
{
vec4 color1 = texture2D(my_texture1, gl_TexCoord[1].st);
vec4 color2 = texture2D(my_texture2, gl_TexCoord[2].st);
if (color1.b > 0.8)
discard;
gl_FragColor = color1;
}
but
uniform sampler2D my_texture1;
uniform sampler2D my_texture2;
void main()
{
vec4 color1 = texture2D(my_texture1, gl_TexCoord[1].st);
vec4 color2 = texture2D(my_texture2, gl_TexCoord[2].st);
if (color2.b > 0.8)
discard;
gl_FragColor = color2;
}
results in a blank screen.
I have a feeling that the problem might lie in how i am passing the texture uniforms to the shader but cant for the life of me work out why the first texture works but the second doesn't. Below is the full program.
from OpenGL.GL import *
from OpenGL.GLU import *
from OpenGL.GLUT import *
from Image import *
from OpenGL.GL.shaders import *
ESCAPE = '\033'
global size
size = 512
def drawQuad(B,T,L,R):
glBegin(GL_QUADS)
glMultiTexCoord2f(GL_TEXTURE1, 0.0, 0.0); glMultiTexCoord2f(GL_TEXTURE2, 0.0, 0.0); glVertex3f(B, L, 1.0); ## Bottom Left Of The Texture and Quad
glMultiTexCoord2f(GL_TEXTURE1, 1.0, 0.0); glMultiTexCoord2f(GL_TEXTURE2, 1.0, 0.0); glVertex3f( T, L, 1.0); ## Bottom Right Of The Texture and Quad
glMultiTexCoord2f(GL_TEXTURE1, 1.0, 1.0); glMultiTexCoord2f(GL_TEXTURE2, 1.0, 1.0); glVertex3f( T, R, 1.0); ## Top Right Of The Texture and Quad
glMultiTexCoord2f(GL_TEXTURE1, 0.0, 1.0); glMultiTexCoord2f(GL_TEXTURE2, 0.0, 1.0); glVertex3f(B, R, 1.0); ## Top Left Of The Texture and Quad
glEnd()
def InitGL(Width, Height):
print "Vendor: " + glGetString(GL_VENDOR)
print "Renderer: " + glGetString(GL_RENDERER)
print "OpenGL Version: " + glGetString(GL_VERSION)
print "Shader Version: " + glGetString(GL_SHADING_LANGUAGE_VERSION)
if not glUseProgram:
print 'Missing Shader Objects!'
sys.exit(1)
global program
program = compileProgram(
compileShader('''
void main()
{
gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
gl_TexCoord[1] = gl_MultiTexCoord1;
gl_TexCoord[2] = gl_MultiTexCoord2;
}
''',GL_VERTEX_SHADER),
compileShader('''
uniform sampler2D my_texture1;
uniform sampler2D my_texture2;
void main()
{
vec4 color1 = texture2D(my_texture1, gl_TexCoord[1].st);
vec4 color2 = texture2D(my_texture2, gl_TexCoord[2].st);
if (color1.b > 0.8)
discard;
gl_FragColor = color1;
}
''',GL_FRAGMENT_SHADER),
)
#bmp texture 1
image = open("rgb.bmp")
ix = image.size[0]
iy = image.size[1]
image = image.tostring("raw", "RGBX", 0, -1)
glActiveTexture(GL_TEXTURE1)
global my_texture1
my_texture1 = glGenTextures(1)
glBindTexture(GL_TEXTURE_2D, my_texture1)
glPixelStorei(GL_UNPACK_ALIGNMENT,1)
glTexImage2D(GL_TEXTURE_2D, 0, 3, ix, iy, 0, GL_RGBA, GL_UNSIGNED_BYTE, image)
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST)
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST)
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL)
glGenerateMipmap(GL_TEXTURE_2D)
#bmp texture 2
image = open("rgb2.bmp")
ix = image.size[0]
iy = image.size[1]
image = image.tostring("raw", "RGBX", 0, -1)
glActiveTexture(GL_TEXTURE2)
global my_texture2
my_texture2 = glGenTextures(1)
glBindTexture(GL_TEXTURE_2D, my_texture2)
glPixelStorei(GL_UNPACK_ALIGNMENT,1)
glTexImage2D(GL_TEXTURE_2D, 0, 3, ix, iy, 0, GL_RGBA, GL_UNSIGNED_BYTE, image)
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST)
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST)
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL)
glGenerateMipmap(GL_TEXTURE_2D)
def DrawGLScene():
global frame, testvar, my_texture1,my_texture2
glEnable(GL_TEXTURE_2D)
glBindTexture(GL_TEXTURE_2D, 0)
glUseProgram(program)
myUniformLocation1 = glGetUniformLocation(program, "my_texture1")
glUniform1i(myUniformLocation1, 1)
myUniformLocation2 = glGetUniformLocation(program, "my_texture2")
glUniform1i(myUniformLocation2, 2)
glViewport(0, 0, size,size)
glClearDepth(1.0)
glClearColor (0.0, 0.0, 0.0, 1.0)
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
glMatrixMode(GL_PROJECTION)
glLoadIdentity()
glOrtho(-1, 1, -1, 1, -30.0, 30.0)
glMatrixMode(GL_MODELVIEW)
glLoadIdentity()
glEnable(GL_DEPTH_TEST)
drawQuad(-1.0,1.0,-1.0,1.0)
glutSwapBuffers()
def keyPressed(*args):
global texturenumber, shadernumber, frame
# If escape is pressed, kill everything.
if args[0] == ESCAPE:
sys.exit()
def main():
global window
glutInit(sys.argv)
glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_DEPTH)
glutInitWindowSize(size,size)
glutInitWindowPosition(0, 0)
window = glutCreateWindow("Multitexturing")
glutDisplayFunc(DrawGLScene)
glutIdleFunc(DrawGLScene)
glutKeyboardFunc(keyPressed)
InitGL(size,size)
glutMainLoop()
if __name__ == "__main__":
print "Press 'ESC' key to quit."
main()

You actually unbind the second texture before using it:
def DrawGLScene():
global frame, testvar, my_texture1,my_texture2
glEnable(GL_TEXTURE_2D)
glBindTexture(GL_TEXTURE_2D, 0)
[...]
After your initialization, texture unit 1 has my_texture1 assigned and texture unit 2 my_texture2. The active texture is still texture 2. So by calling glBindTexture(GL_TEXTURE_2D, 0) you unbind the texture from the active texture unit 2.
What you shoud do is this:
def DrawGLScene():
global frame, testvar, my_texture1,my_texture2
glActiveTexture(GL_TEXTURE1)
glBindTexture(GL_TEXTURE_2D, my_texture1)
glActiveTexture(GL_TEXTURE2)
glBindTexture(GL_TEXTURE_2D, my_texture2)
[...]
You could also simply remove the last four lines (after global frame, testvar, my_texture1,my_texture2) since your init routine takes care of this. However, if you bind and unbind any other textures in your code you have to do the texture unit activation and texture binding as above.