This topic is now archived and is closed to further replies.

OpenGL Plasma in Opengl Help(Not sine)

This topic is 5026 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

Hi, I am trying to convert some pygame plasma code to Opengl. However I cannot figure out how to do a getpixel command in Opengl. Any guides, help or directions will be appreciated. Here is the pygame code : import pygame, sys from Numeric import * from RandomArray import * import random # Global Values ScreenRes=array((640,480)) global screen global color #global colorarray pygame.init() screen=pygame.display.set_mode(ScreenRes,0,8) #screen.set_palette([[0,0,0],[0,255,0],[255,255,255]]) #we will use this to setup our palette for plasma def ramp(rs,re,gs,ge,bs,be,startcol,endcol): n=1 nadd=int(255/(endcol-startcol)) for i in range(startcol,endcol): r=int((((rs-re)*n)/255)+re) g=int((((gs-ge)*n)/255)+ge) b=int((((bs-be)*n)/255)+be) screen.set_palette_at(i,[r,g,b]) n=n+nadd # #Rotate the palette # def rotatepalette(): y=screen.get_palette() y = list(y) for s in range(254): x = y.pop(1) y.append(x) screen.set_palette(tuple(y)) pygame.display.update() # #Put down the starting points # def startplasma(x0,y0,x1,y1): screen.lock() screen.set_at((x0,y0),(random.randint(0,255)+1)) screen.set_at((x1,y0),(random.randint(0,255)+1)) screen.set_at((x0,y1),(random.randint(0,255)+1)) screen.set_at((x1,y1),(random.randint(0,255)+1)) screen.unlock() # #Calculate the new color # def newcolor(x0,y0,x,y,x1,y1): # c=screen.get_at((x,y)) if screen.get_at((x,y)) <> (0,0,0,255): return() color=(x1-x0)+(y1-y0) color=random.randint(0,(color*2))-color a=screen.map_rgb(screen.get_at((x0,y0))) b=screen.map_rgb(screen.get_at((x1,y1))) color=color+int((a+b+1)/2) if color < 1: color=1 elif color > 254: color=254 screen.set_at((x,y),color) # #Do the actual plasma calculations # #START PROCEDURE doblock def doblock(x0,y0,x1,y1): if ((x1-x0)<2) and ((y1-y0)<2): return() x=int((x0+x1+1)/2) y=int((y0+y1+1)/2) newcolor(x0,y0,x,y0,x1,y0) newcolor(x1,y0,x1,y,x1,y1) newcolor(x0,y1,x,y1,x1,y1) newcolor(x0,y0,x0,y,x0,y1) a=screen.map_rgb(screen.get_at((x0,y0))) b=screen.map_rgb(screen.get_at((x1,y0))) c=screen.map_rgb(screen.get_at((x1,y1))) d=screen.map_rgb(screen.get_at((x0,y1))) e=2 color=int((a+b+c+d+e)/4) screen.set_at((x,y),color) doblock(x0,y0,x,y) doblock(x,y0,x1,y) doblock(x,y,x1,y1) doblock(x0,y,x,y1) #END PROCEDURE doblock ramp(255,000,000,000,000,000,1,63) ramp(000,255,000,000,000,000,63,126) ramp(000,000,255,000,000,255,126,189) ramp(000,000,000,255,000,000,189,256) #while 1: # for event in pygame.event.get(): # if event.type == pygame.QUIT: # sys.exit() x0=0 y0=0 x1=639 y1=479 startplasma(x0,y0,x1,y1) doblock(0,0,639,479) pygame.display.update() while 1: rotatepalette() for event in pygame.event.get(): if event.type == pygame.QUIT: sys.exit() It takes a while to draw the plasma on slower systems. This is the reason why I want to port it to Opengl. (Pardon the english, it is not my native language) All of us were put on earth to do a certain amount of work. I am so far behind I will never die.

Share this post

Link to post
Share on other sites
First, this belongs to the OpenGL forum, not the graphics forum.
Second, there are no functions in OpenGL for getting and setting individual pixels (IIRC), since that is extremely inefficient, and further OpenGL was not meant to be a 2D API (although it can be used as such). There are, however, function for getting and setting a rectagle of pixels, glGet/SetPixels or some such thing.
And finally, it is highly unrecommended to read anything back from the hardware, since it is very slow. Instead, you should keep a copy of the plasma image in system memory, update it as normal, and then blit to the hardware buffer with glSetPixels (or whatever its name is). Other than that, you can try to put the plasma calculations in a pixel shader, but those are usually not available on low-end systems.

Michael K.,
Co-designer and Graphics Programmer of "The Keepers"

We come in peace... surrender or die!

Share this post

Link to post
Share on other sites

  • Similar Content

    • By xhcao
      Does sync be needed to read texture content after access texture image in compute shader?
      My simple code is as below,
      glBindImageTexture(0, texture[0], 0, GL_FALSE, 3, GL_READ_ONLY, GL_R32UI);
      glBindImageTexture(1, texture[1], 0, GL_FALSE, 4, GL_WRITE_ONLY, GL_R32UI);
      glDispatchCompute(1, 1, 1);
      // Does sync be needed here?
      glBindFramebuffer(GL_READ_FRAMEBUFFER, framebuffer);
                                     GL_TEXTURE_CUBE_MAP_POSITIVE_X + face, texture[1], 0);
      glReadPixels(0, 0, kWidth, kHeight, GL_RED_INTEGER, GL_UNSIGNED_INT, outputValues);
      Compute shader is very simple, imageLoad content from texture[0], and imageStore content to texture[1]. Does need to sync after dispatchCompute?
    • By Jonathan2006
      My question: is it possible to transform multiple angular velocities so that they can be reinserted as one? My research is below:
      // This works quat quaternion1 = GEQuaternionFromAngleRadians(angleRadiansVector1); quat quaternion2 = GEMultiplyQuaternions(quaternion1, GEQuaternionFromAngleRadians(angleRadiansVector2)); quat quaternion3 = GEMultiplyQuaternions(quaternion2, GEQuaternionFromAngleRadians(angleRadiansVector3)); glMultMatrixf(GEMat4FromQuaternion(quaternion3).array); // The first two work fine but not the third. Why? quat quaternion1 = GEQuaternionFromAngleRadians(angleRadiansVector1); vec3 vector1 = GETransformQuaternionAndVector(quaternion1, angularVelocity1); quat quaternion2 = GEQuaternionFromAngleRadians(angleRadiansVector2); vec3 vector2 = GETransformQuaternionAndVector(quaternion2, angularVelocity2); // This doesn't work //quat quaternion3 = GEQuaternionFromAngleRadians(angleRadiansVector3); //vec3 vector3 = GETransformQuaternionAndVector(quaternion3, angularVelocity3); vec3 angleVelocity = GEAddVectors(vector1, vector2); // Does not work: vec3 angleVelocity = GEAddVectors(vector1, GEAddVectors(vector2, vector3)); static vec3 angleRadiansVector; vec3 angularAcceleration = GESetVector(0.0, 0.0, 0.0); // Sending it through one angular velocity later in my motion engine angleVelocity = GEAddVectors(angleVelocity, GEMultiplyVectorAndScalar(angularAcceleration, timeStep)); angleRadiansVector = GEAddVectors(angleRadiansVector, GEMultiplyVectorAndScalar(angleVelocity, timeStep)); glMultMatrixf(GEMat4FromEulerAngle(angleRadiansVector).array); Also how do I combine multiple angularAcceleration variables? Is there an easier way to transform the angular values?
    • By dpadam450
      I have this code below in both my vertex and fragment shader, however when I request glGetUniformLocation("Lights[0].diffuse") or "Lights[0].attenuation", it returns -1. It will only give me a valid uniform location if I actually use the diffuse/attenuation variables in the VERTEX shader. Because I use position in the vertex shader, it always returns a valid uniform location. I've read that I can share uniforms across both vertex and fragment, but I'm confused what this is even compiling to if this is the case.
      #define NUM_LIGHTS 2
      struct Light
          vec3 position;
          vec3 diffuse;
          float attenuation;
      uniform Light Lights[NUM_LIGHTS];
    • By pr033r
      I have a Bachelor project on topic "Implenet 3D Boid's algorithm in OpenGL". All OpenGL issues works fine for me, all rendering etc. But when I started implement the boid's algorithm it was getting worse and worse. I read article ( inspirate from another code (here: but it still doesn't work like in tutorials and videos. For example the main problem: when I apply Cohesion (one of three main laws of boids) it makes some "cycling knot". Second, when some flock touch to another it scary change the coordination or respawn in origin (x: 0, y:0. z:0). Just some streng things. 
      I followed many tutorials, change a try everything but it isn't so smooth, without lags like in another videos. I really need your help. 
      My code (optimalizing branch):
      Exe file (if you want to look) and models folder (for those who will download the sources):
      Thanks for any help...

    • By Andrija
      I am currently trying to implement shadow mapping into my project , but although i can render my depth map to the screen and it looks okay , when i sample it with shadowCoords there is no shadow.
      Here is my light space matrix calculation
      mat4x4 lightViewMatrix; vec3 sun_pos = {SUN_OFFSET * the_sun->direction[0], SUN_OFFSET * the_sun->direction[1], SUN_OFFSET * the_sun->direction[2]}; mat4x4_look_at(lightViewMatrix,sun_pos,player->pos,up); mat4x4_mul(lightSpaceMatrix,lightProjMatrix,lightViewMatrix); I will tweak the values for the size and frustum of the shadow map, but for now i just want to draw shadows around the player position
      the_sun->direction is a normalized vector so i multiply it by a constant to get the position.
      player->pos is the camera position in world space
      the light projection matrix is calculated like this:
      mat4x4_ortho(lightProjMatrix,-SHADOW_FAR,SHADOW_FAR,-SHADOW_FAR,SHADOW_FAR,NEAR,SHADOW_FAR); Shadow vertex shader:
      uniform mat4 light_space_matrix; void main() { gl_Position = light_space_matrix * transfMatrix * vec4(position, 1.0f); } Shadow fragment shader:
      out float fragDepth; void main() { fragDepth = gl_FragCoord.z; } I am using deferred rendering so i have all my world positions in the g_positions buffer
      My shadow calculation in the deferred fragment shader:
      float get_shadow_fac(vec4 light_space_pos) { vec3 shadow_coords = / light_space_pos.w; shadow_coords = shadow_coords * 0.5 + 0.5; float closest_depth = texture(shadow_map, shadow_coords.xy).r; float current_depth = shadow_coords.z; float shadow_fac = 1.0; if(closest_depth < current_depth) shadow_fac = 0.5; return shadow_fac; } I call the function like this:
      get_shadow_fac(light_space_matrix * vec4(position,1.0)); Where position is the value i got from sampling the g_position buffer
      Here is my depth texture (i know it will produce low quality shadows but i just want to get it working for now):
      sorry because of the compression , the black smudges are trees ...
      EDIT: Depth texture attachment:
  • Popular Now