I'm making a game for iOS using GLKit (OpenGL ES 2), and would like to use VBOs and VAOs as I think they would increase performance quite a lot (and Instruments is recommending it when I test my app in it).
I have a lot of textured objects that don't actually change position, size, texture etc, so I would assume VBOs would help.
At the moment I am using arrays of GLKVector2 to store vertex and texture coordinate data, and I'm not quite sure how to go from here to VBOs.
Can anyone help with this?
Cheers,
Nick.
You can pass them directly to glBufferData (), like this:
GLKVector2 objects[k];
// ... Fill out your objects vertices in objects
GLuint buffer = 0;
glGenBuffers (1, &buffer);
glBindBuffer (GL_ARRAY_BUFFER, buffer);
glBufferData (GL_ARRAY_BUFFER, sizeof (objects), objects, GL_STATIC_DRAW);
glEnableClientState (GL_VERTEX_ARRAY);
glVertexPointer (2, GL_FLOAT, sizeof (GLKVertex2), 0);
This tell OpenGL to generate a buffer and bind it. glBufferData() actually uploads it to the card. The call to glVertexPointer () says where you want to start pulling vertices from in the array. The pointer in the last parameter becomes an offset when you're using VBOs.
EDIT: Sorry - filled in some details. Had a brain fart. See here for details.
Related
I am working hard on a new iOS game that is drawn only with procedurally generated lines. All is working well, except for a few strange hiccups with drawing some primitives.
I am at a point where I need to implement text, and the characters are set up to be a series of points in an array. When I go to draw the points (which are CGPoints) some of the drawing modes are working funny.
effect.transform.modelviewMatrix = matrix;
[effect prepareToDraw];
glEnableVertexAttribArray(GLKVertexAttribPosition);
glVertexAttribPointer(GLKVertexAttribPosition, 2, GL_FLOAT, 0, 0, &points);
glDrawArrays(GL_POINTS, 0, ccc);
I am using this code to draw from the array, and when the mode is set to GL_LINE_LOOP or GL_LINE_STRIP all works well. But if I set it to GL_POINTS, I get a gpus_ReturnGuiltyForHardwareRestert error. And if I try GL_LINES it just doesn't draw anything.
What could possibly be going on?
When you draw with GL_POINTS in ES2 or ES3, you need to specify gl_PointSize in the vertex shader or you'll get undefined behavior (ugly rendering on device at best, the crash you're seeing at worst). The vertex shader GLKBaseEffect uses doesn't do gl_PointSize, so you can't use it with GL_POINTS. You'll need to implement your own shaders. (For a starting point, try the ones in the "OpenGL Game" template you get when creating a new Xcode project, or using the Xcode Frame Debugger to look at the GLSL that GLKBaseEffect generates.)
GL_LINES should work fine as long as you're setting an appropriate width with glLineWidth() in client code.
I'm currently new to OpenGL ES and am self teaching myself how to program iOS games. I'm currently playing with a project that I would like to put a HUD over with some custom text. I don't want to do this using a UILabel and currently have no idea how to use Quads to cut up a png or such full of text and attach them to normal text to be used for display. I would like the end result to be providing a simple string to a command/method and the output to be displayed using the textures/bitmap for the quad. Say glPrint("Hello World");. Would anyone be able to guide me in the proper direction? There doesn't seem to be a single good tutorial on how to do this for OpenGL ES 2.0 (just OpenGL). I also want to try to avoid using 3rd party APIs. I really need/want to understand how to tackle this.
When I was getting started with OpenGL ES for my current 2D project I used Ray's tutorial, which helped me get a handle on rendering textured 2D quads. In conjunction with his 3D OpenGL ES tutorial, you might be able to piece together what you want to do. Note that you probably wouldn't render every single quad separately like in the tutorial, as that is very inefficient. Instead, you would gather all of the vertices of the characters into two big arrays/vertex buffers and batch render the characters. The basic flow for rendering each frame would probably look like this: pass a normal perspective projection matrix for 3D rendering, get your vertex information for your 3D scene to your shaders somehow, render the 3D scene. This part you've already done. For the text, immediately after, pass an orthogonal projection matrix in, bind your font texture (generally generated earlier with the GLKTextureLoader class) to the active texture unit, generate two big arrays of texture and geometric vertices for the characters/update VBOs if the text has changed, pass that in, and then batch render all of the letters at once using either glDrawArrays or glDrawElements (which requires indices).
Also, as I'm also new at using OpenGL, some of this may be wrong/inefficient. I've yet to use OpenGL ES to render anything 3D, so I'm not sure what other state changes (enabling, disabling, etc) besides a different projection matrix might be needed between rendering your 3D scene and the 2D scene (text).
It seems that drawing text using only OpenGL is a relatively difficult and tedious task, so if you just want to render a HUD overlay displaying frame rates and other things you are much better off using UILabels and saving yourself the trouble, especially if your project is not very complex. This also prevents you from having to deal with wrapping, kerning, font sizes, colors, different languages and a load of other stuff that greatly complicates text rendering if you need anything more complex.
Rather than tracking the location of each letter, why not use Core Graphics to draw your entire string into a bitmap, then upload that as a texture? You'd just need to get the dimensions from your bitmap to know what size quad to draw for that text string.
Within my open source GPUImage framework, I have an input class called a GPUImageUIElement that does something similar. The relevant code from that input is as follows:
CGSize layerPixelSize = [self layerSizeInPixels];
GLubyte *imageData = (GLubyte *) calloc(1, (int)layerPixelSize.width * (int)layerPixelSize.height * 4);
CGColorSpaceRef genericRGBColorspace = CGColorSpaceCreateDeviceRGB();
CGContextRef imageContext = CGBitmapContextCreate(imageData, (int)layerPixelSize.width, (int)layerPixelSize.height, 8, (int)layerPixelSize.width * 4, genericRGBColorspace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
CGContextTranslateCTM(imageContext, 0.0f, layerPixelSize.height);
CGContextScaleCTM(imageContext, layer.contentsScale, -layer.contentsScale);
[layer renderInContext:imageContext];
CGContextRelease(imageContext);
CGColorSpaceRelease(genericRGBColorspace);
glBindTexture(GL_TEXTURE_2D, outputTexture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, (int)layerPixelSize.width, (int)layerPixelSize.height, 0, GL_BGRA, GL_UNSIGNED_BYTE, imageData);
free(imageData);
This code takes a CALayer (either directly or from the backing layer of a UIView) and renders its contents to a texture. I've already initialized the texture before this, so the code sets up a bitmap context, renders the layer into that context using -renderInContext:, and then uploads that bitmap to the texture for use in OpenGL ES.
The helper method -layerSizeInPixels just accounts for the current Retina scale factor as follows:
- (CGSize)layerSizeInPixels;
{
CGSize pointSize = layer.bounds.size;
return CGSizeMake(layer.contentsScale * pointSize.width, layer.contentsScale * pointSize.height);
}
If you used a UILabel for your view and had it autosize to fit its text, you could set the text on it, use the above to render and upload your texture, and then take the pixel size of the element to determine your quad size. However, it would probably be more efficient to just draw the text yourself using -drawAtPoint:withFont:fontForSize: or the like with an NSString.
Using Core Graphics to render your text makes it easy to manipulate the text as an NSString and use all of Core Graphics' typesetting capabilities instead of rolling your own.
I've almost finished my app. One of the views uses GLKit. I just have a problem with memory. Basically what happens is that when GLKView is displayed, the memory consumption constantly rises (seen with Instruments). At a certain point it obviously crashes.
I don't know much about GLKit, so I hope you can help me.
The problem is a 3d arrow that I'm displaying. If I don't draw it, all the other things don't create any problem.
This is the header file that contains the arrow vertex data:
#import <GLKit/GLKit.h>
struct arrowVertexData
{
GLKVector3 vertex;
GLKVector3 normal;
GLKVector2 texCoord;
};
typedef struct arrowVertexData arrowVertexData;
typedef arrowVertexData* vertexDataPtr;
static const arrowVertexData MeshVertexData[] = {
{/*v:*/{{-0.000004, 0.0294140, -0.0562387}}, /*n:*/{{0.000000, 1.000000, 0.000000}}, /*t:*/{{0.500000, 0.333333}}},
... etc...
And this is the draw code:
- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect {
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
[self.arrowEffect prepareToDraw];
//glGenVertexArraysOES(1, &arrowVertexArray);
//glBindVertexArrayOES(arrowVertexArray);
glGenBuffers(1, &arrowVertexBuffer);
glBindBuffer(GL_ARRAY_BUFFER, arrowVertexBuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(MeshVertexData), MeshVertexData, GL_STATIC_DRAW);
glEnableVertexAttribArray(GLKVertexAttribPosition);
glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, sizeof(arrowVertexData), 0);
glEnableVertexAttribArray(GLKVertexAttribNormal);
glVertexAttribPointer(GLKVertexAttribNormal, 3, GL_FLOAT, GL_TRUE, sizeof(arrowVertexData), (void *)offsetof(arrowVertexData, normal));
glBindVertexArrayOES(arrowVertexArray);
// Render the object with GLKit
glDrawArrays(GL_TRIANGLES, 0, sizeof(MeshVertexData) / sizeof(arrowVertexData));
//reset buffers
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
//disable atttributes
glDisableVertexAttribArray(GLKVertexAttribNormal);
glDisableVertexAttribArray(GLKVertexAttribPosition);
}
Any suggestion?
Thank you very much for you help!
You are creating a new vertex buffer (VBO) each time drawInRect is called, and never deleting them. GLGenBuffers and GLBindBuffer set up and a new buffer and make it current, but the real damage is done with GLBufferData, which copies the data into the new buffer.
glBindBuffer(GL_ARRAY_BUFFER, 0); resets GL to not use the buffer, and glDisableVertexAttribArray(GLKVertexAttribPosition); tells GL not to look for position data in a buffer anymore, but neither of these calls does anything to free the memory. If you wanted to free the memory each time, you would need to call GLDeleteBuffers(1, &arrowVertexBuffer); to free the memory.
A better approach would be to generate the buffer once at startup and delete it when terminating, and hang on to arrowVertexBuffer, rebinding and unbinding it each time through as needed, as sell as reseting the pointers, assuming other parts of your program are modifying GL state.
It looks like you also started down the path of using a Vertex Array Object (VAO), which would be another way to capture state once for reuse, although it may be better to wait until you have the VBO working correctly before attempting that. Both VBOs and VAOs are methods for caching state that evolved over time to reduce the load each time through your rendering loop, but VAOs cast a much broader net, which could make it trickier to get it right.
As a general suggestion, you may be able to get more attention for a question like this by adding a more general and popular tag, such as [Open GL].
Another debugging tool you should definitely try is OpenGL Profiler. If you did not install it with XCode, look it up in the documentation and you should find a link to download the graphic tools package. The resources window will allow you to track the buffer objects in use.
Have you tried running the static analyzer in Xcode?
It's very good at pointing out allocated memory that isn't released and that kind of thing.
To use it hold the mouse down on the "Run" button and select "Analyze" from the drop down list.
If it does find anything it usually points them out in blue and you can see the lines tracing back to where memory is being allocated and not released, etc...
Let me know if that has any effect.
I can't find much info on whether drawing from multiple vertex buffers is supported on opengl es 2.0 (i.e use one vertex buffer for position data and another for normal, colors etc). This page http://developer.apple.com/library/ios/#documentation/3DDrawing/Conceptual/OpenGLES_ProgrammingGuide/TechniquesforWorkingwithVertexData/TechniquesforWorkingwithVertexData.html and listing 9.4 in particular implies you should be able to, but I can't get it to work on my program. Code for the offending draw call:
glBindBuffer(GL_ARRAY_BUFFER, mPositionBuffer->openglID);
glVertexAttribPointer(0, 4, GL_FLOAT, 0, 16, NULL);
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, mTexCoordBuffer->openglID);
glVertexAttribPointer(1, 2, GL_FLOAT, 0, 76, NULL);
glEnableVertexAttribArray(1);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, mIndexBuffer->openglID);
glDrawElements(GL_TRIANGLES, 10788, GL_UNSIGNED_SHORT, NULL);
This draw call will stall or crash with EXC_BAD_ACCESS on the simulator, and gives very weird behavior on the device (opengl draws random triangles or presents previously rendered frames). No opengl call ever returns an error, and I've inspected the vertex buffers extensively and am confident they have the correct sizes and data.
Has anyone successfully rendered using multiple vertex buffers and can share their experience on why this might not be working? Any info on where to start debugging stalled/failed draw calls that don't return any error code would be greatly appreciated.
Access violations generally mean that you are trying to draw more triangles than you have allocated in a buffer. The way you've set up buffers is perfectly fine and should work, I would be checking if your parameters are set properly:
http://www.opengl.org/sdk/docs/man/xhtml/glVertexAttribPointer.xml
http://www.opengl.org/sdk/docs/man/xhtml/glDrawElements.xml
I think your issue is either that you've switched offset and stride in your glVertexAttribPointer calls, or you've miscounted the number of indices you're drawing
Yes, you can use multiple vertex buffer objects (VBOs) for a single draw. The OpenGL ES 2.0 spec says so in section 2.9.1.
Do you really have all those hard-coded constants in your code? Where did that 76 come from?
If you want help debugging, you need to post the code that initializes your buffers (the code that calls glGenBuffers and glBufferData). You should also post the stack trace of EXC_BAD_ACCESS.
It might also be easier to debug if you drew something simpler, like one triangle, instead of 3596 triangles.
I'm wanting to port some image processing work to OpenGL for performance using OpenGL ES. I've got a very simple thresholding algorithm in place but I'd like to combine additional filters to the image (such as contrast).
My first thought would be to complete this by using multiple fragment shaders. However, I'd like to do this pretty quickly so would this cause a lot of state change? The only method I've read about is to do this by working on a texture and then calling 'use program' multiple times.
Is there a more efficient way to do this? Ideally, I'd like to perform a contrast stretch and a histogram balance as part of the steps.
Unless I can combine this into a single shader would an FBO work for me here?
I'm a bit new to OpenGL (in case you couldn't tell).
Thanks!
Simon
You can't "merge" fragment shader unless you do it manually, so the only sane choice is to do "ping-pong" rendering using FBOs. You have 2 FBOs, draw to one and read from another, then switch FBOs and repeat, switching fragment shaders between rendering.
Ping pong rendering is quite nice for this purpose, actually! Here's a code sample that works within LibGDX, where there is a 'batch' object that actually draws to the screen, the input to which we can capture with FrameBuffers:
FrameBuffer ping = fbo; // the framebuffer containing your rendered texture
for (ShaderProgram shader : shaders) {
pong.clear();
pong.begin();
batch.begin();
batch.setShader(shader);
batch.draw(ping.getColorBufferTexture(), 0, 0, width, height);
batch.end();
pong.end();
ping = pong;
}
batch.begin();
batch.draw(pong.getColorBufferTexture(), 0, 0, width, height);
batch.end();
The clear call to pong (in my case, making a new framebuffer) is expensive, so preallocating might offer some speedups. This is more of a followup to Matias' answer than an answer in itself, but wouldn't fit in a comment.