Sign in to follow this  

OpenGL Re-Order Elements in a Vector

This topic is 1415 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

This may be more of a general programming question. I'm currently batching all of my sprites' vertices in one giant, interleaved vertex array. I don't use VBOs for this right now since I am supporting OpenGL ES 2.0, and data is likely to change frequently bit over time. Since I'm drawing everything in one draw call, I'll need to have my vertices sorted within the array in a back-to-forward fashion. All of my vertices are in stored in an STL vector. I'm trying to figure out an efficient way of doing this, though. Whenever I add a sprite to my batch, I can just insert the sprites based on depth, but what if I had to move 4 vertices making up one of my sprites back 8 vertices? Should I just insert a copy of my sprite's vertices, then erase the original copy from the vector?

Share this post

Link to post
Share on other sites

the best I can think of is to scan unordered buffer of sprites, finding ouy their indexes order upon many sort alogrithms available , and than build an index buffer to render the unordered buffer by. This way you can have the buffer static, keeping its footprint in CPU, as in many sprite/particles implementations the count of particle elements do not vary. If in your very case a once ordered buffer does not change unless being added a sprite, what seems unlikely, this given approach is valid as well. One drawback of this approach is that the generated indicies will not be adjency friendly. If you want to have unindexed buffer instead, use this approach and by ordered indexes recreate the buffer instead to be ordered upon those indexes. Once added a sprite, you will have to move sprites behind it and expand the buffer, but you would not have to do it if you index the buffer, but it will be just adjency unfriendly.

Share this post

Link to post
Share on other sites
The above is correct in using and sorting an index buffer, however you will still not be able to use a static vertex buffer if you manually update the vertex locations with matrix multiplies (since you are not using instancing and keeping everything in one buffer).
Frankly, by this point you might be better off just making a single draw call for each sprite after sorting the order of calls locally. You should at least benchmark it with a static VBO.

In either case you should be using VBO’s and triple-buffering them. Most mobile devices supporting OpenGL ES 2.0 have built-in triple-buffering on the back-buffer and forced v-sync, so triple-buffering your vertex/index buffers should result in little-to-no lag.

L. Spiro

Share this post

Link to post
Share on other sites


to use a static vertex buffer if you manually update the vertex locations with matrix multiplies

true, but one can move the tranformation to vertex function, which outperforms CPU tranforming, since paralel pipelines eat it up, and yet, it allows one to have the buffer static. This is yet possible only if Vincent_M will not expand amount of verticies/sprites, keeping them in constant amount. I myself am using a very tripy aproach. I transform sprite quads by the help of their object space z - what allows mi to have any procedural animation, transforming all verticies by the uniformal matrix. Drawing sprites/particles by an indexed buffer is rather vital too, since buffer can contain 100 of them, but with indicies you can specify how many to draw, with what uniform transformation. For example uniform buffer limits you to 128 matricies, so you draw first 128, and then the next ones, in few batches. But I rather use procedural aproach, in case I am drawing fire, not light flies of course.

Share this post

Link to post
Share on other sites
Sign in to follow this  

  • Similar Content

    • By _OskaR
      I have an OpenGL application but without possibility to wite own shaders.
      I need to perform small VS modification - is possible to do it in an alternative way? Do we have apps or driver modifictions which will catch the shader sent to GPU and override it?
    • 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...

  • Popular Now