I have a number of textures loaded using GLKTextureLoader. If I bind any of the loaded textures statically, each texture works as expected.
But I am trying to bind a random texture each glDrawArrays call, but the texture bound is always the same.
GLuint vbo = vboIDs[emitterNum];
GLKMatrix4 projectionMatrix = GLKMatrix4MakeScale(1.0f, aspectRatio, 1.0f);
glUseProgram(emitterShader[emitterNum].program);
glEnable(GL_TEXTURE_2D);
glActiveTexture (GL_TEXTURE0);
//Note: valid texture names are 0-31, but in my code I store texture names returned in an array and use them. Use arc4random here for simplicity
glBindTexture(GL_TEXTURE_2D, arc4random_uniform(31)); //use a random texture name
//glBindTexture(GL_TEXTURE_2D, 2); //If I use this line instead of the line above, it will draw texture 2, or any number I specify
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glUniformMatrix4fv(emitterShader[emitterNum].uProjectionMatrix, 1, 0, projectionMatrix.m);
//I set a number of uniforms such as:
glUniform1f(emitterShader[emitterNum].uTime, timeCurrentFrame);
glUniform1i(emitterShader[emitterNum].uTexture, 0);
//I set a number of vertex arrays such as:
glEnableVertexAttribArray(emitterShader[emitterNum].aShade);
glVertexAttribPointer(emitterShader[emitterNum].aShade, // Set pointer
4, // four components per particle (vec4)
GL_FLOAT, // Data is floating point type
GL_FALSE, // No fixed point scaling
sizeof(Particles), // No gaps in data
(void*)(offsetof(Particles, shade))); // Start from "shade" offset within bound buffer
GLsizei rowsToUse = emitters[emitterNum]->rows;
//Draw the arrays
glDrawArrays(GL_POINTS, 0, rowsToUse );
//Then clean up
glBindTexture(GL_TEXTURE_2D, 0);
glUseProgram(0);
glDisable(GL_TEXTURE_2D);
glBindBuffer(GL_ARRAY_BUFFER, 0);
I have tried putting the texture calls in various places, like where shown and direct before the glDrawArrays command, but no matter what - I can't make it bind to different textures unless done so statically.
Related
Say we have an object and we want to create multiple objects and move them independently based some algorithm.
Here is what is the process I am using:
Create a structure with the geometry of the object
Create an array of vertice buffers using the geometry of the object
Now in the rendering routine, I need to go through each one of those objects and alter their position based on a specific algorithm.
To accomplish this I need to get the current location of the object to compute the new position.
How can I get the current location of a vertice buffer? Clearly, I do not want to store outside the program all locations of the object since they are inside the vertice buffer.
EDIT: This is the code I am using to store and retrieve data from the model matrix of each object
// Set up Code
- (void)setupGL
{
[EAGLContext setCurrentContext:self.context];
[self loadShaders];
glEnable(GL_DEPTH_TEST);
for( int i; i<num_objects; i++) {
glGenVertexArraysOES(1, &_objectArray[i]);
glBindVertexArrayOES(_objectArray[i]);
glGenBuffers(1, &_objectBuffer[i]);
glBindBuffer(GL_ARRAY_BUFFER, _objectBuffer[i]);
glBufferData(GL_ARRAY_BUFFER, sizeof(objectData), objectData, GL_STATIC_DRAW);
glEnableVertexAttribArray(....);
glVertexAttribPointer(......, 3, GL_FLOAT, GL_FALSE, 24, BUFFER_OFFSET(0));
}
glBindVertexArrayOES(0);
}
//********************************************************
// Rendering Code
- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect
{
glUseProgram(_program);
for(int i=0; i<num_objects; i++) {
glBindVertexArrayOES(_objectArray[i]);
// Get Previous data
GLint uMatrix = glGetUniformLocation(_program, "modelMatrix");
glGetUniformfv(_program, uMatrix, dataOfCurrentObject);
// Get Previous data
... transform dataOfCurrentObject based on an algorithm and create newDataOfCurrentObject
// Update object with new data and draw
glUniformMatrix4fv(uMatrix, 1, 0, newDataOfCurrentObject);
glDrawArrays(GL_TRIANGLES, 0, 36);
}
}
The problem I have now is that the dataOfCurrentObject for object 'i' is identical to the newDataOfCurrentObject for object 'i-1'. In other words it appears that the code keeps track of only one model matrix for all objects, or it does not read correctly the model matrix of a specific object. Any ideas?
The simplest method that gets used is to set the object's position in the Model Matrix, and upload that object's appropriate Model Matrix as a Uniform each time you draw a new object. The [pseudo-]code would look like this:
for(game_object object : game_object_list) {
glUniformMatrix4f(modelMatrixUniformLocation, 1, false, object->model_matrix);
object->draw();
}
And when you need to update the object's position:
for(game_object object : game_object_list) {
object->model_matrix = Matrix.identity();
/*Any transformations that need to take place here*/
object->model_matrix = object->model_matrix.transpose(/*x*/, /*y*/);
/*Any other transformations that need to take place*/
}
Exactly what you put in there will vary depending on your needs. If you're programming a 2D game, you probably don't need a 4x4 model matrix. But the basic logic should be identical to what you eventually use.
You don't have to read anything back from your vertex buffers. You just need to keep in your application the tranform you need and pass it as uniform for every object.
For example if you need to translate the object, keep the modelViewMatrix in and every frame apply trasformation to the previous matrix :
GLKMatrix4 modelViewMatrix;
...
modelViewMatrix = GLKMatrix4Identity;
...
-(void) render {
modelViewMatrix = GLKMatrix4Translate(modelViewMatrix, deltaX, deltaY, deltaZ);
glUniformMatrix4fv(_modelViewUniform, 1,0, modelViewMatrix.m);
}
So you just need to keep reference to your objects modelView matrices and apply your transformations accordingly.
If you want to read data back from your vertex buffers (gpu) to your application you have to use Transform Feedback which is a bit more advanced technique and it is used when you modify your vertexes in the vertex shader and you need the results back. (It is not needed for your case).
Do a good deed and help get someone (me) out of their misery, since it's New Year's Eve soon. I'm working on an iOS app, a coloring book for kids and I haven't stumbled upon OpenGL before (more precisely OpenGLES 2.0) so there's a big chance there's stuff I don't actually get in my code.
One of the tasks is to not let the brush spill out of the contour in which the user started drawing.
After reading and understanding some OpenGL basics, I found that using the stencil buffer is the right solution. This is my stencil buffer setup:
glClearStencil(0);
//clear the stencil
glClear(GL_STENCIL_BUFFER_BIT);
//disable writing to color buffer
glColorMask( GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE );
//disable depth buffer
glDisable(GL_DEPTH_TEST);
//enable writing to stencil buffer
glEnable(GL_STENCIL_TEST);
glStencilFunc(GL_NEVER, 1, 0xFF);
glStencilOp(GL_REPLACE, GL_REPLACE, GL_REPLACE);
[self drawStencil];
//re-enable color buffer
glColorMask( GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE );
//only draw where there is a 1
glStencilFunc(GL_EQUAL, 1, 1);
//keep the pixels in the stencil buffer
glStencilOp( GL_KEEP, GL_KEEP, GL_KEEP );
Right now, I'm just trying to draw a square in the stencil buffer and see if I can limit my drawing only to that square. This is the method drawing the square:
- (void)drawStencil
{
// Create a renderbuffer
GLuint renderbuffer;
glGenRenderbuffers(1, &renderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, renderbuffer);
[context renderbufferStorage:GL_RENDERBUFFER fromDrawable:(CAEAGLLayer*)self.layer];
// Create a framebuffer
GLuint framebuffer;
glGenFramebuffers(1, &framebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_STENCIL_ATTACHMENT, GL_RENDERBUFFER, renderbuffer);
// Clear
glClearColor(1, 1, 1, 1);
glClear(GL_COLOR_BUFFER_BIT);
// Read vertex shader source
NSString *vertexShaderSource = [NSString stringWithContentsOfFile:[[NSBundle mainBundle] pathForResource:#"VertexShader" ofType:#"vsh"] encoding:NSUTF8StringEncoding error:nil];
const char *vertexShaderSourceCString = [vertexShaderSource cStringUsingEncoding:NSUTF8StringEncoding];
// Create and compile vertex shader
GLuint _vertexShader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(_vertexShader, 1, &vertexShaderSourceCString, NULL);
glCompileShader(_vertexShader);
// Read fragment shader source
NSString *fragmentShaderSource = [NSString stringWithContentsOfFile:[[NSBundle mainBundle] pathForResource:#"FragmentShader" ofType:#"fsh"] encoding:NSUTF8StringEncoding error:nil];
const char *fragmentShaderSourceCString = [fragmentShaderSource cStringUsingEncoding:NSUTF8StringEncoding];
// Create and compile fragment shader
GLuint _fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(_fragmentShader, 1, &fragmentShaderSourceCString, NULL);
glCompileShader(_fragmentShader);
// Create and link program
GLuint program = glCreateProgram();
glAttachShader(program, _vertexShader);
glAttachShader(program, _fragmentShader);
glLinkProgram(program);
// Use program
glUseProgram(program);
// Define geometry
GLfloat square[] = {
-0.5, -0.5,
0.5, -0.5,
-0.5, 0.5,
0.5, 0.5};
//Send geometry to vertex shader
const char *aPositionCString = [#"a_position" cStringUsingEncoding:NSUTF8StringEncoding];
GLuint aPosition = glGetAttribLocation(program, aPositionCString);
glVertexAttribPointer(aPosition, 2, GL_FLOAT, GL_FALSE, 0, square);
glEnableVertexAttribArray(aPosition);
// Draw
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
// Present renderbuffer
[context presentRenderbuffer:GL_RENDERBUFFER];
}
So much code and nothing happens... I can draw relentlessly wherever I want without a single stencil test stopping me.
What can I do? How do I check if the stencil buffer has something drawn inside it? If there's a missing puzzle for any of you, I will happily share any other parts of the code.
Any help is greatly appreciated! This has been torturing me for a while now. I will be forever in your debt!
UPDATE
I got the contour thing to work but I didn't use the stencil buffer. I created masks for every drawing area and textures for each mask which I loaded in the fragment shader along with the brush texture. When I tap on an area, I iterate through the array of masks and see which one was selected and bind the mask texture. I will make another post on SO with a more appropriate title and explain it there.
The way you allocate the renderbuffer storage looks problematic:
[context renderbufferStorage:GL_RENDERBUFFER fromDrawable:(CAEAGLLayer*)self.layer];
The documentation says about this method:
The width, height, and internal color buffer format are derived from the characteristics of the drawable object.
The way I understand it, since your "drawable object" will normally be a color buffer, this will create a color renderbuffer. But you need a renderbuffer with stencil format in your case. I'm not sure if there's a way to do this with a utility method in the context class (the documentation says something about "overriding the internal color buffer format"), but the easiest way is probably to simply call the corresponding OpenGL function directly:
glRenderbufferStorage(GL_RENDERBUFFER, GL_STENCIL_INDEX8, width, height);
If you want to use your own FBO for this rendering, you will also need to create a color buffer for it, and attach it to the FBO. Otherwise you're not really producing any rendering output.
Instead of creating a new FBO, it might be easier to make sure that the default framebuffer has a stencil buffer, and render to it directly. To do this, you can request a stencil buffer for your GLKView derived view by making this call during setup:
[view setDrawableStencilFormat: GLKViewDrawableStencilFormat8];
So I have been trying to create a trailing particle effect (seen here) with OpenGL ES 2.0. Unfortunately it appears that the OpenGL command (accumulation buffer) that makes this possible is not available in OpenGL es. This means that it will be necessary to go the LONG way.
This topic described a possible method to do such a thing. However I am quite confused about how to store things inside a buffer and combine buffers. So my thought was to do the following.
Draw the current frame into a texture using a buffer that writes to a texture
Draw the previous frames (but faded) into another buffer.
Put step 1 ontop of step 2. And display that.
Save whatever is displayed for use next frame.
My understanding so far is that buffers store pixel data in the same way textures do, just that buffers can more easily be drawn to using shaders.
So the idea would probably be to render to a buffer THEN move it into a texture.
One theory for doing this that I found is this
In retrospect, you should create two FBOs (each with its own texture);
using the default framebuffer isn't reliable (the contents aren't
guaranteed to be preserved between frames).
After binding the first FBO, clear it then render the scene normally.
Once the scene has been rendered, use the texture as a source and
render it to the second FBO with blending (the second FBO is never
cleared). This will result in the second FBO containing a mix of the
new scene and what was there before. Finally, the second FBO should be
rendered directly to the window (this can be done by rendering a
textured quad, similarly to the previous operation, or by using
glBlitFramebuffer).
Essentially, the first FBO takes the place of the default framebuffer
while the second FBO takes the place of the accumulation buffer.
In summary:
Initialisation:
For each FBO:
- glGenTextures
- glBindTexture
- glTexImage2D
- glBindFrameBuffer
- glFramebufferTexture2D
Each frame:
glBindFrameBuffer(GL_DRAW_FRAMEBUFFER, fbo1) glClear glDraw* // scene
glBindFrameBuffer(GL_DRAW_FRAMEBUFFER, fbo2) glBindTexture(tex1)
glEnable(GL_BLEND) glBlendFunc glDraw* // full-screen quad
glBindFrameBuffer(GL_DRAW_FRAMEBUFFER, 0)
glBindFrameBuffer(GL_READ_FRAMEBUFFER, fbo2) glBlitFramebuffer
unfortunately it didnt have quite enough code (especially for initialization to get me started).
But I have tried, and so far all I have gotten is a disappointing blank screen. I dont really know what I am doing, so probably this code is quite wrong.
var fbo1:GLuint = 0
var fbo2:GLuint = 0
var tex1:GLuint = 0
Init()
{
//...Loading shaders OpenGL etc.
//FBO 1
glGenFramebuffers(1, &fbo1)
glBindFramebuffer(GLenum(GL_FRAMEBUFFER), fbo1)
//Create texture for shader output
glGenTextures(1, &tex1)
glBindTexture(GLenum(GL_TEXTURE_2D), tex1)
glTexImage2D(GLenum(GL_TEXTURE_2D), 0, GL_RGB, width, height, 0, GLenum(GL_RGB), GLenum(GL_UNSIGNED_BYTE), nil)
glFramebufferTexture2D(GLenum(GL_FRAMEBUFFER), GLenum(GL_COLOR_ATTACHMENT0), GLenum(GL_TEXTURE_2D), tex1, 0)
//FBO 2
glGenFramebuffers(1, &fbo2)
glBindFramebuffer(GLenum(GL_FRAMEBUFFER), fbo2)
//Create texture for shader output
glGenTextures(1, &tex1)
glBindTexture(GLenum(GL_TEXTURE_2D), tex1)
glTexImage2D(GLenum(GL_TEXTURE_2D), 0, GL_RGB, width, height, 0, GLenum(GL_RGB), GLenum(GL_UNSIGNED_BYTE), nil)
glFramebufferTexture2D(GLenum(GL_FRAMEBUFFER), GLenum(GL_COLOR_ATTACHMENT0), GLenum(GL_TEXTURE_2D), tex1, 0)
}
func drawFullScreenTex()
{
glUseProgram(texShader)
let rect:[GLint] = [0, 0, GLint(width), GLint(height)]
glBindTexture(GLenum(GL_TEXTURE_2D), tex1)
//Texture is allready
glTexParameteriv(GLenum(GL_TEXTURE_2D), GLenum(GL_TEXTURE_CROP_RECT_OES), rect)
glDrawTexiOES(0, 0, 0, width, height)
}
fun draw()
{
//Prep
glBindFramebuffer(GLenum(GL_DRAW_FRAMEBUFFER), fbo1)
glClearColor(0, 0.1, 0, 1.0)
glClear(GLbitfield(GL_COLOR_BUFFER_BIT))
//1
glUseProgram(pointShader);
passTheStuff() //Just passes in uniforms
drawParticles(glGetUniformLocation(pointShader, "color"), size_loc: glGetUniformLocation(pointShader, "pointSize")) //Draws particles
//2
glBindFramebuffer(GLenum(GL_DRAW_FRAMEBUFFER), fbo2)
drawFullScreenTex()
//3
glBindFramebuffer(GLenum(GL_DRAW_FRAMEBUFFER), 0)
glBindFramebuffer(GLenum(GL_READ_FRAMEBUFFER), fbo2)
glBlitFramebuffer(0, 0, width, height, 0, 0, width, height, GLbitfield(GL_COLOR_BUFFER_BIT), GLenum(GL_NEAREST))
}
BTW here are some sources I found useful.
Site 1
Site 2
Site 3
Site 4
My main question is: Could someone please write out the code for this. I think I understand the theory involved, but I have spent so much time trying in vain to apply it.
If you want a place to start I have the Xcode project that draws dots, and has a blue one that moves across the screen periodically here, also the code that isn't working is in their as well.
Note: If you are going to write code you can use any language c++, java, swift, objective-c it will be perfectly fine. As long as it is for OpenGL-ES
You call glGenTextures(1, &tex1) twice with the same variable tex1. This overwrites the variable. When you later call glBindTexture(GLenum(GL_TEXTURE_2D), tex1), it does not bind the texture corresponding to fbo1, but rather that of fbo2. You need a different texture for every fbo.
As for a reference, below is a sample from a working program of mine which uses multiple FBOs and renders to texture.
GLuint fbo[n];
GLuint tex[n];
init() {
glGenFramebuffers(n, fbo);
glGenTextures(n, tex);
for (int i = 0; i < n; ++i) {
glBindFramebuffer(GL_FRAMEBUFFER, fbo[i]);
glBindTexture(GL_TEXTURE_2D, tex[i]);
glTexImage2D( GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glFramebufferTexture2D(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, tex[i], 0);
}
}
render() {
glBindFramebuffer(GL_DRAW_FRAMEBUFFER, fbo[0]);
glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
// Draw scene into buffer 0
glBindFrameBuffer(GL_DRAW_FRAMEBUFFER, fbo[1]);
glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
glBindTexture(cbo[0]);
//Draw full screen tex
...
glBindFrameBuffer(GL_DRAW_FRAMEBUFFER, 0);
glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
glBindTexture(cbo[n - 1]);
// Draw to screen
return;
}
A few notes. In order to get it to work I had to add the texture parameters.
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
This is because on my system they defaulted to GL_NEAREST_MIPMAP_LINEAR. This did not work for the FBO texture, as no mipmap was generated. Set these to anything you like.
Also, make sure you have textures enabled with
glEnable(GL_TEXTURE_2D)
I hope this will help.
I create a little application in WebGL, I have two objects which move, a cube and a sphere.
I modify objects with shaders, each object have it shader. So I want update objects on the display at determine time, for this I use drawElements function.
For each object I have a buffer which contains indices of faces in vertices buffer :
gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, this.indexBuffer);
gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint16Array(indices), gl.STREAM_DRAW);
indexCount = indices.length;
indices is an array which contains values of indices of each faces. (3 values per face, we work with triangles).
So, after this, for draw triangles of the object I do :
gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, indexBuffer);
gl.drawElements(gl.TRIANGLES, indexCount, gl.UNSIGNED_SHORT, 0);
But I have nothing on the screen, and I have this warning :
WebGL: INVALID_OPERATION: drawElements: attribs not setup correctly
What's could be my error ?
Thanks
I think you missed codes which link javascript vertex buffer to shader's attributes before drawElements().
e.g:
gl.bindBuffer(gl.ARRAY_BUFFER, meshVertexPositionBuffer);
gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute,
meshVertexPositionBuffer.itemSize, gl.FLOAT, false, 0, 0);
gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, meshIndexBuffer);
gl.drawElements(gl.TRIANGLES, meshIndexBuffer.numberOfItems, gl.UNSIGNED_SHORT, 0);
I am having trouble understanding how to use VAO's in OpenGL ES2 (on iOS) and getting them to work.
My current rendering setup looks like this (in pseudocode):
Initialization:
foreach VBO:
glGenBuffers();
Rendering a frame:
// Render VBO 1
glClear(color | depth);
glBindBuffer(GL_ARRAY_BUFFER, arrayVBO1);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexVBO1);
foreach vertex attribute:
glVertexAttribPointer();
glEnableVertexAttribArray();
glBufferData(GL_ARRAY_BUFFER, ...);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, ...);
glDrawElements(GL_TRIANGLE_STRIP, ...);
// Render VBO 2
glClear(color | depth);
glBindBuffer(GL_ARRAY_BUFFER, arrayVBO2);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexVBO2);
foreach vertex attribute:
glVertexAttribPointer();
glEnableVertexAttribArray();
glBufferData(GL_ARRAY_BUFFER, ...);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, ...);
glDrawElements(GL_TRIANGLE_STRIP, ...);
This works fine, however, both VBO's have exactly the same interleaved vertex attribute struct, and as you can see I'm setting up and enabling each attribute every frame for every VBO. Instruments complains about redundant calls to glVertexAttribPointer() and glEnableVertexAttribArray(), but when I move one of them or both to the initialization phase I either get a EXC_BAD_ACCESS when calling glDrawElements or nothing is drawn.
My question is whether I need to do this every frame, why it doesn't work if I don't, and how I would use VAO's to solve this.
Sorry for the dredge, but I'm procrastinating and you keep topping my google search. I'm sure you've solved it by now...
The correct way is to only update the buffers when the data changes, not every frame. Ideally, you would only update the part of the buffer that changed. Also, Attribute Pointers are offsets into the buffer if a buffer is bound.
Initialisation:
glGenBuffers()
foreach VBO:
glBufferData()
Updates / Animation, etc:
glMapBuffer() //or something like this
buffer->vertex = vec3(1,2,3) // etc
glUnmapBuffer()
And Render:
glBindFBO()
glClear(color | depth);
glBindBuffer(GL_ARRAY_BUFFER, arrayVBO1)
glVertexAttribPointer(GL_VERTEX,..., 0) // Buffer Offset = 0
glVertexAttribPointer(GL_TEXCOORD,..., sizeof(vertex)) // Buffer Offset = size of vertex
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexVBO1);
glEnableVertexAttribArray(..., 0) // Buffer Offset = 0
glBindBuffer(0); // Unbind buffers, you don't need them here
glDrawElements(GL_TRIANGLE_STRIP, ...);
Hope that helps.