Related
I want to get a trails effect. I am drawing particles to a frame buffer. which is never cleared (accumulates draw calls). Fading out is done by drawing a black quad with small alpha, for example 0.0, 0.0, 0.0, 0.1. A two step process, repeated per frame:
- drawing a black quad
- drawing particles at new positions
All works nice, the moving particles produce long trails EXCEPT the black quad does not clear the FBO down to perfect zero. Faint trails remain forever (e.g. buffer's RGBA = 4,4,4,255).
I assume the problem starts when a blending function multiplies small values of FBO's 8bit RGBA (destination color) by, for example (1.0-0.1)=0.9 and rounding prevents further reduction. For example 4 * 0.9 = 3.6 -> rounded back to 4, for ever.
Is my method (drawing a black quad) inherently useless for trails? I cannot find a blend function that could help, since all of them multiply the DST color by some value, which must be very small to produce long trails.
The trails are drawn using a code:
GLuint drawableFBO;
glGetIntegerv(GL_FRAMEBUFFER_BINDING, &drawableFBO);
glBindFramebuffer(GL_FRAMEBUFFER, FBO); /// has an attached texture glFramebufferTexture2D -> FBOTextureId
glEnable(GL_BLEND);
glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
glUseProgram(fboClearShader);
glUniform4f(fboClearShader.uniforms.color, 0.0, 0.0, 0.0, 0.1);
glUniformMatrix4fv(fboClearShader.uniforms.modelViewProjectionMatrix, 1, 0, mtx.m);
glBindVertexArray(fboClearShaderBuffer);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
glUseProgram(particlesShader);
glUniformMatrix4fv(shader.uniforms.modelViewProjectionMatrix, 1, 0, mtx.m);
glUniform1f(shader.uniforms.globalAlpha, 0.9);
glBlendFunc(GL_ONE, GL_ONE);
glBindTexture(particleTextureId);
glBindVertexArray(particlesBuffer);
glDrawArrays(GL_TRIANGLES, 0, 1000*6);
/// back to drawable buffer
glBindFramebuffer(GL_FRAMEBUFFER, drawableFBO);
glUseProgram(fullScreenShader);
glBindVertexArray(screenQuad);
glBlendFuncGL_ONE dFactor:GL_ONE];
glBindTexture(FBOTextureId);
glDrawArrays(GL_TRIANGLES, 0, 6);
Blending is not only defined by the by the blend function glBlendFunc, it is also defined by the blend equation glBlendEquation.
By default the source value and the destination values are summed up, after they are processed by the blend function.
Use a blend function which subtracts a tiny value from the destination buffer, so the destination color will slightly decreased in each frame and finally becomes 0.0.
The the results of the blend equations is clamped to the range [0, 1].
e.g.
dest_color = dest_color - RGB(0.01)
The blend equation which subtracts the source color form the destination color is GL_FUNC_REVERSE_SUBTRACT:
float dec = 0.01f; // should be at least 1.0/256.0
glEnable(GL_BLEND);
glBlendEquation(GL_FUNC_REVERSE_SUBTRACT);
glBlendFunc(GL_ONE, GL_ONE);
glUseProgram(fboClearShader);
glUniform4f(fboClearShader.uniforms.color, dec, dec, dec, 0.0);
Updated with more explanation around my confusion
(This is how a non-graphics developer imagines the rendering process!)
I specify a 2x2 sqaure to be drawn in by way of two triangles. I'm going to not talk about the triangle anymore. Square is a lot better. Let's say the square gets drawn in one piece.
I have not specified any units for my drawing. The only places in my code that I do something like that is: canvas size (set to 1x1 in my case) and the viewport (i always set this to the dimensions of my output texture).
Then I call draw().
What happens is this: that regardless of the size of my texture (being 1x1 or 10000x10000) all my texels are filled with data (color) that I returned from my frag shader. This is working each time perfectly.
So now I'm trying to explain this to myself:
The GPU is only concerned with coloring the pixels.
Pixel is the smallest unit that the GPU deals with (colors).
Depending on how many pixels my 2x2 square is mapped to, I should be running into one of the following 3 cases:
The number of pixels (to be colored) and my output texture dims match one to one: In this ideal case, for each pixel, there would be one value assigned to my output texture. Very clear to me.
The number of pixels are fewer than my output texture dims. In this case, I should expect that some of the output texels to have exact same value (which is the color of the pixel the fall under). For instance if the GPU ends up drawing 16x16 pixels and my texture is 64x64 then I'll have blocks of 4 texel which get the same value. I have not observed such case regardless of the size of my texture. Which means there is never a case where we end up with fewer pixels (really hard to imagine -- let's keep going)
The number of pixels end up being more than the number of texels. In this case, the GPU should decide which value to assign to my texel. Would it average out the pixel colors? If the GPU is coloring 64x64 pixels and my output texture is 16x16 then I should expect that each texel gets an average color of the 4x4 pixels it contains. Anyway, in this case my texture should be completely filled with values I didn't intend specifically for them (like averaged out) however this has not been the case.
I didn't even talk about how many times my frag shader gets called because it didn't matter. The results would be deterministic anyway.
So considering that I have never run into 2nd and 3rd case where the values in my texels are not what I expected them the only conclusion I can come up with is that the whole assumption of the GPU trying to render pixels is actually wrong. When I assign an output texture to it (which is supposed to stretch over my 2x2 square all the time) then the GPU will happily oblige and for each texel will call my frag shader. Somewhere along the line the pixels get colored too.
But the above lunatistic explanation also fails to answer why I end up with no values in my texels or incorrect values if I stretch my geometry to 1x1 or 4x4 instead of 2x2.
Hopefully the above fantastic narration of the GPU coloring process has given you clues as to where I'm getting this wrong.
Original Post:
We're using WebGL for general computation. As such we create a rectangle and draw 2 triangles in it. Ultimately what we want is the data inside the texture mapped to this geometry.
What I don't understand is if I change the rectangle from (-1,-1):(1,1) to say (-0.5,-0.5):(0.5,0.5) suddenly data is dropped from the texture bound to the framebuffer.
I'd appreciate if someone makes me understand the correlations. The only places that real dimensions of the output texture come into play are the call to viewPort() and readPixels().
Below are relevant pieces of code for you to see what I'm doing:
... // canvas is created with size: 1x1
... // context attributes passed to canvas.getContext()
contextAttributes = {
alpha: false,
depth: false,
antialias: false,
stencil: false,
preserveDrawingBuffer: false,
premultipliedAlpha: false,
failIfMajorPerformanceCaveat: true
};
... // default geometry
// Sets of x,y,z (for rectangle) and s,t coordinates (for texture)
return new Float32Array([
-1.0, 1.0, 0.0, 0.0, 1.0, // upper left
-1.0, -1.0, 0.0, 0.0, 0.0, // lower left
1.0, 1.0, 0.0, 1.0, 1.0, // upper right
1.0, -1.0, 0.0, 1.0, 0.0 // lower right
]);
...
const geometry = this.createDefaultGeometry();
gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
gl.bufferData(gl.ARRAY_BUFFER, geometry, gl.STATIC_DRAW);
... // binding to the vertex shader attribs
gl.vertexAttribPointer(positionHandle, 3, gl.FLOAT, false, 20, 0);
gl.vertexAttribPointer(textureCoordHandle, 2, gl.FLOAT, false, 20, 12);
gl.enableVertexAttribArray(positionHandle);
gl.enableVertexAttribArray(textureCoordHandle);
... // setting up framebuffer; I set the viewport to output texture dimensions (I think this is absolutely needed but not sure)
gl.bindTexture(gl.TEXTURE_2D, texture);
gl.bindFramebuffer(gl.FRAMEBUFFER, this.framebuffer);
gl.framebufferTexture2D(
gl.FRAMEBUFFER, // The target is always a FRAMEBUFFER.
gl.COLOR_ATTACHMENT0, // We are providing the color buffer.
gl.TEXTURE_2D, // This is a 2D image texture.
texture, // The texture.
0); // 0, we aren't using MIPMAPs
gl.viewport(0, 0, width, height);
... // reading from output texture
gl.bindTexture(gl.TEXTURE_2D, texture);
gl.framebufferTexture2D(
gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, texture,
0);
gl.readPixels(0, 0, width, height, gl.FLOAT, gl.RED, buffer);
new answer
I'm just saying the same thing yet again (3rd time?)
Copied from below
WebGL is destination based. That means it's going to iterate over the pixels of the line/point/triangle it's drawing and for each point call the fragment shader and ask 'what value should I store here`?
It's destination based. It's going to draw each pixel exactly once. For that pixel it's going to ask "what color should I make this"
destination based loop
for (let i = start; i < end; ++i) {
fragmentShaderFunction(); // must set gl_FragColor
destinationTextureOrCanvas[i] = gl_FragColor;
You can see in the loop above there is no setting any random destination. There is no setting any part of destination twice. It's just going to run from start to end and exactly once for each pixel in the destination between start and end ask what color it should make that pixel.
How to do you set start and end? Again, to make it simple let's assume a 200x1 texture so we can ignore Y. It works like this
vertexShaderFunction(); // must set gl_Position
const start = clipspaceToArrayspaceViaViewport(viewport, gl_Position.x);
vertexShaderFunction(); // must set gl_Position
const end = clipspaceToArrayspaceViaViewport(viewport, gl_Position.x);
for (let i = start; i < end; ++i) {
fragmentShaderFunction(); // must set gl_FragColor
texture[i] = gl_FragColor;
}
see below for clipspaceToArrayspaceViaViewport
What is viewport? viewport is what you set when you called `gl.viewport(x, y, width, height)
So, set gl_Position.x to -1 and +1, viewport.x to 0 and viewport.width = 200 (the width of the texture) then start will be 0, end will be 200
set gl_Position.x to .25 and .75, viewport.x to 0 and viewport.width = 200 (the width of the texture). The start will be 125 and end will be 175
I honestly feel like this answer is leading you down the wrong path. It's not remotely this complicated. You don't have to understand any of this to use WebGL IMO.
The simple answer is
You set gl.viewport to the sub rectangle you want to affect in your destination (canvas or texture it doesn't matter)
You make a vertex shader that somehow sets gl_Position to clip space coordinates (they go from -1 to +1) across the texture
Those clip space coordinates get converted to the viewport space. It's basic math to map one range to another range but it's mostly not important. It's seems intuitive that -1 will draw to the viewport.x pixel and +1 will draw to the viewport.x + viewport.width - 1 pixel. That's what "maps from clip space to the viewport settings means".
It's most common for the viewport settings to be (x = 0, y = 0, width = width of destination texture or canvas, height = height of destination texture or canvas)
So that just leaves what you set gl_Position to. Those values are in clip space just like it explains in this article.
You can make it simple by doing if you want by converting from pixel space to clip space just like it explains in this article
zeroToOne = someValueInPixels / destinationDimensions;
zeroToTwo = zeroToOne * 2.0;
clipspace = zeroToTwo - 1.0;
gl_Position = clipspace;
If you continue the articles they'll also show adding a value (translation) and multiplying by a value (scale)
Using just those 2 things and a unit square (0 to 1) you can choose any rectangle on the screen. Want to effect 123 to 127. That's 5 units so scale = 5, translation = 123. Then apply the math above to convert from pixels to clips space and you'll get the rectangle you want.
If you continue further though those articles you'll eventually get the point where that math is done with matrices but you can do that math however you want. It's like asking "how do I compute the value 3". Well, 1 + 1 + 1, or 3 + 0, or 9 / 3, or 100 - 50 + 20 * 2 / 30, or (7^2 - 19) / 10, or ????
I can't tell you how to set gl_Position. I can only tell you make up whatever math you want and set it to *clip space* and then give an example of converting from pixels to clipspace (see above) as just one example of some possible math.
old answer
I get that this might not be clear I don't know how to help. WebGL draws lines, points, or triangles two a 2D array. That 2D array is either the canvas, a texture (as a framebuffer attachment) or a renderbuffer (as a framebuffer attachment).
The size of the area is defined by the size of the canvas, texture, renderbuffer.
You write a vertex shader. When you call gl.drawArrays(primitiveType, offset, count) you're telling WebGL to call your vertex shader count times. Assuming primitiveType is gl.TRIANGLES then for every 3 vertices generated by your vertex shader WebGL will draw a triangle. You specify that triangle by setting gl_Position in clip space.
Assuming gl_Position.w is 1, Clip space goes from -1 to +1 in X and Y across the destination canvas/texture/renderbuffer. (gl_Position.x and gl_Position.y are divided by gl_Position.w) which is not really important for your case.
To convert back to actually pixels your X and Y are converted based on the settings of gl.viewport. Let's just do X
pixelX = ((clipspace.x / clipspace.w) * .5 + .5) * viewport.width + viewport.x
WebGL is destination based. That means it's going to iterate over the pixels of the line/point/triangle it's drawing and for each point call the fragment shader and ask 'what value should I store here`?
Let's translate that to JavaScript in 1D. Let's assume you have an 1D array
const dst = new Array(100);
Let's make a function that takes a start and end and sets values between
function setRange(dst, start, end, value) {
for (let i = start; i < end; ++i) {
dst[i] = value;
}
}
You can fill the entire 100 element array with 123
const dst = new Array(100);
setRange(dst, 0, 99, 123);
To set the last half of the array to 456
const dst = new Array(100);
setRange(dst, 50, 99, 456);
Let's change that to use clip space like coordinates
function setClipspaceRange(dst, clipStart, clipEnd, value) {
const start = clipspaceToArrayspace(dst, clipStart);
const end = clipspaceToArrayspace(dst, clipEnd);
for (let i = start; i < end; ++i) {
dst[i] = value;
}
}
function clipspaceToArrayspace(array, clipspaceValue) {
// convert clipspace value (-1 to +1) to (0 to 1)
const zeroToOne = clipspaceValue * .5 + .5;
// convert zeroToOne value to array space
return Math.floor(zeroToOne * array.length);
}
This function now works just like the previous one except takes clip space values instead of array indices
// fill entire array with 123
const dst = new Array(100);
setClipspaceRange(dst, -1, +1, 123);
Set the last half of the array to 456
setClipspaceRange(dst, 0, +1, 456);
Now abstract one more time. Instead of using the array's length use a setting
// viewport looks like `{ x: number, width: number} `
function setClipspaceRangeViaViewport(dst, viewport, clipStart, clipEnd, value) {
const start = clipspaceToArrayspaceViaViewport(viewport, clipStart);
const end = clipspaceToArrayspaceViaViewport(viewport, clipEnd);
for (let i = start; i < end; ++i) {
dst[i] = value;
}
}
function clipspaceToArrayspaceViaViewport(viewport, clipspaceValue) {
// convert clipspace value (-1 to +1) to (0 to 1)
const zeroToOne = clipspaceValue * .5 + .5;
// convert zeroToOne value to array space
return Math.floor(zeroToOne * viewport.width) + viewport.x;
}
Now to fill the entire array with 123
const dst = new Array(100);
const viewport = { x: 0, width: 100; }
setClipspaceRangeViaViewport(dst, viewport, -1, 1, 123);
Set the last half of the array to 456 there are now 2 ways. Way one is just like the previous using 0 to +1
setClipspaceRangeViaViewport(dst, viewport, 0, 1, 456);
You can also set the viewport to start half way through the array
const halfViewport = { x: 50, width: 50; }
setClipspaceRangeViaViewport(dst, halfViewport, -1, +1, 456);
I don't know if that was helpful or not.
The only other thing to add is instead of value replace that with a function that gets called every iteration to supply value
function setClipspaceRangeViaViewport(dst, viewport, clipStart, clipEnd, fragmentShaderFunction) {
const start = clipspaceToArrayspaceViaViewport(viewport, clipStart);
const end = clipspaceToArrayspaceViaViewport(viewport, clipEnd);
for (let i = start; i < end; ++i) {
dst[i] = fragmentShaderFunction();
}
}
Note this is the exact same thing that is said in this article and clearified somewhat in this article.
Im having trouble displaying pixel based art (think retro tiles and art) on OpenGL Es 1.1 on the iPhones.
Tiles are represented using 8bytes (1 byte for each row) with each bit representing a pixel being set or not.
For example a tile with the number 8:
0 0 0 0 0 0 0 0 ->
0 0 1 1 1 0 0 0 -> xxx
0 1 0 0 0 1 0 0 -> x x
0 1 0 0 0 1 0 0 -> x x
0 0 1 1 1 0 0 0 -> xxx
0 1 0 0 0 1 0 0 -> x x
0 1 0 0 0 1 0 0 -> x x
0 0 1 1 1 0 0 0 -> xxx
Converting this to OpenGL on iPhone using
glDrawArrays(GL_POINTS, 0, 64);
The logic is correct, but the problem is it doesn't give the retro effect. I was looking for more of a blocky/retro style. I read that i can turn off pixel smoothing which would cause pixels to be displayed as squares.(i think it was GL_Disable(POINT_SMOOTH), but not sure if this effects ES since nothing changed.)
Possible solutions i found to relating problems:
use a frame buffer to render to a smaller resolution and then scale it up in the render buffer. I don't know how this is done or if it'll work.
Create an image from the pixels, create a texture from that image and finally render that texture.
Possible solutions i thought off:
For each pixel, draw two pixels instead both horizontally and vertically.
Draw each pixel as a square using triangles.
Use GLPointSize - gives a correct effect when set to 2, but coordinates are then messed up. Aligning becomes harder.
Ultimately i would like the tiles to be presented:
This is more of me understanding how OpenGL and pixels work, and I'm using a gameboy emulator to work this out. If someone thinks the correct way is to create the graphics manually and load them as textures, its not the feasible answer.
There are quite a few ways of doing this and I would suggest the first one you already found. Draw the scene to a smaller buffer and then redraw it a canvas.
What you are looking here for is a FBO (frame buffer object). Find some examples on how to create a FBO and attach a texture to it. This will create a buffer for you with any dimensions you will input. Some common issues here are that you will most likely need a POT texture (a power of 2 dimensions: 2, 4, 8, 16... So 64x128 buffer for instance) so to control a different size you should use viewport which will then use only a part of the buffer you need.
So in the end this will create a low resolution texture which can be used to draw to the canvas (view). How you draw to it something you should experiment with. The points may not be the best solution, even in your case of a buffer I would use lines between the points you defined in your example. At this point you must choose to draw with or without the antialias. To enable it look for the multisampling on iOS.
After you have the texture to which the shape is drawn you will need to redraw it to the view. This is pretty much drawing a full-screen texture. Again you have multiple ways of drawing it. The most powerful tool here are the texture parameters: Using nearest will discard all the color interpolations and the squares should be visible; using linear (or trilinear) will do some interpolation and the result will probably be nearer to what you want to achieve. Then you may again play around with multisampling to create antialiasing and get a better result.
So the powers here are:
Different FBO buffer sizes
Antialiasing on the FBO
Texture parameters
Antialiasing when redrawing to canvas
As for the FBO this is one of the easiest things to do:
Generate frame buffer (glGenFramebuffers)
Bind the frame buffer (glBindFramebuffer)
Create a texture (glGenTextures) and bind it (glBindTexture)
Set texture data glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, twidth, theight, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
Attach the texture to the frame buffer glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture.textureID, 0);
Now when you draw to the texture you need to bind the FBO frame buffer and when you draw to the main buffer just bind that frame buffer.
Since this is quite a broad answer (as is the question)... If you will be implementing this and will have additional questions or issues it will be best to create a separate questions and probably link them in the comments.
Good luck.
Im not sure if my question was not clear, but to draw pixels to screen you have to create a texture and pass in the pixel data to it, then render that texture onto the screen. It would be the equivalent of glDrawPixels.
The code would be:
#define W 255,255,255
#define G 192,192,192
//8 x 8 tile with 3 bytes for each pixel RGB format
GLubyte pixels[8 * 8 * 3] = {
W,W,W,W,W,W,W,W,
W,W,G,G,G,W,W,W,
W,G,W,W,W,G,W,W,
W,G,W,W,W,G,W,W,
W,W,G,G,G,W,W,W,
W,G,W,W,W,G,W,W,
W,G,W,W,W,G,W,W,
W,W,G,G,G,W,W,W
};
somewhere in setup:
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glGenTextures(1, &tex);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, tex);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 8, 8, 0, GL_RGB, GL_UNSIGNED_BYTE, pixels);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
Then draw the texture as usual:
glActiveTexture(GL_TEXTURE0);
glUniform1i([program uniformLocation:#"s_texture"], 0);
glBindTexture(GL_TEXTURE_2D, tex);
glEnableVertexAttribArray(positionAttrib);
glVertexAttribPointer(positionAttrib, 2, GL_FLOAT, GL_FALSE, 0, v);
glEnableVertexAttribArray(texAttrib);
glVertexAttribPointer(texAttrib, 2, GL_FLOAT, GL_FALSE, 0, t);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_BYTE, i);
I am working on a drawing application and I am noticing significant differences in textures loaded on a 32-bit iPad vs. a 64-bit iPad.
Here is the texture drawn on a 32-bit iPad:
Here is the texture drawn on a 64-bit iPad:
The 64-bit is what I desire, but it seems like maybe it is losing some data?
I create a default brush texture with this code:
UIGraphicsBeginImageContext(CGSizeMake(64, 64));
CGContextRef defBrushTextureContext = UIGraphicsGetCurrentContext();
UIGraphicsPushContext(defBrushTextureContext);
size_t num_locations = 3;
CGFloat locations[3] = { 0.0, 0.8, 1.0 };
CGFloat components[12] = { 1.0,1.0,1.0, 1.0,
1.0,1.0,1.0, 1.0,
1.0,1.0,1.0, 0.0 };
CGColorSpaceRef myColorspace = CGColorSpaceCreateDeviceRGB();
CGGradientRef myGradient = CGGradientCreateWithColorComponents (myColorspace, components, locations, num_locations);
CGPoint myCentrePoint = CGPointMake(32, 32);
float myRadius = 20;
CGGradientDrawingOptions options = kCGGradientDrawsBeforeStartLocation | kCGGradientDrawsAfterEndLocation;
CGContextDrawRadialGradient (UIGraphicsGetCurrentContext(), myGradient, myCentrePoint,
0, myCentrePoint, myRadius,
options);
CFRelease(myGradient);
CFRelease(myColorspace);
UIGraphicsPopContext();
[self setBrushTexture:UIGraphicsGetImageFromCurrentImageContext()];
UIGraphicsEndImageContext();
And then actually set the brush texture like this:
-(void) setBrushTexture:(UIImage*)brushImage{
// save our current texture.
currentTexture = brushImage;
// first, delete the old texture if needed
if (brushTexture){
glDeleteTextures(1, &brushTexture);
brushTexture = 0;
}
// fetch the cgimage for us to draw into a texture
CGImageRef brushCGImage = brushImage.CGImage;
// Make sure the image exists
if(brushCGImage) {
// Get the width and height of the image
GLint width = CGImageGetWidth(brushCGImage);
GLint height = CGImageGetHeight(brushCGImage);
// Texture dimensions must be a power of 2. If you write an application that allows users to supply an image,
// you'll want to add code that checks the dimensions and takes appropriate action if they are not a power of 2.
// Allocate memory needed for the bitmap context
GLubyte* brushData = (GLubyte *) calloc(width * height * 4, sizeof(GLubyte));
// Use the bitmatp creation function provided by the Core Graphics framework.
CGContextRef brushContext = CGBitmapContextCreate(brushData, width, height, 8, width * 4, CGImageGetColorSpace(brushCGImage), kCGImageAlphaPremultipliedLast);
// After you create the context, you can draw the image to the context.
CGContextDrawImage(brushContext, CGRectMake(0.0, 0.0, (CGFloat)width, (CGFloat)height), brushCGImage);
// You don't need the context at this point, so you need to release it to avoid memory leaks.
CGContextRelease(brushContext);
// Use OpenGL ES to generate a name for the texture.
glGenTextures(1, &brushTexture);
// Bind the texture name.
glBindTexture(GL_TEXTURE_2D, brushTexture);
// Set the texture parameters to use a minifying filter and a linear filer (weighted average)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
// Specify a 2D texture image, providing the a pointer to the image data in memory
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, brushData);
// Release the image data; it's no longer needed
free(brushData);
}
}
Update:
I've updated CGFloats to be GLfloats with no success. Maybe there is an issue with this rendering code?
if(frameBuffer){
// draw the stroke element
[self prepOpenGLStateForFBO:frameBuffer];
[self prepOpenGLBlendModeForColor:element.color];
CheckGLError();
}
// find our screen scale so that we can convert from
// points to pixels
GLfloat scale = self.contentScaleFactor;
// fetch the vertex data from the element
struct Vertex* vertexBuffer = [element generatedVertexArrayWithPreviousElement:previousElement forScale:scale];
glLineWidth(2);
// if the element has any data, then draw it
if(vertexBuffer){
glVertexPointer(2, GL_FLOAT, sizeof(struct Vertex), &vertexBuffer[0].Position[0]);
glColorPointer(4, GL_FLOAT, sizeof(struct Vertex), &vertexBuffer[0].Color[0]);
glTexCoordPointer(2, GL_FLOAT, sizeof(struct Vertex), &vertexBuffer[0].Texture[0]);
glDrawArrays(GL_TRIANGLES, 0, (GLint)[element numberOfSteps] * (GLint)[element numberOfVerticesPerStep]);
CheckGLError();
}
if(frameBuffer){
[self unprepOpenGLState];
}
The vertex struct is the following:
struct Vertex{
GLfloat Position[2]; // x,y position
GLfloat Color [4]; // rgba color
GLfloat Texture[2]; // x,y texture coord
};
Update:
The issue does not actually appear to be 32-bit, 64-bit based, but rather something different about the A7 GPU and GL drivers. I found this out by running a 32-bit build and 64-bit build on the 64-bit iPad. The textures ended up looking exactly the same on both builds of the app.
I would like you to check two things.
Check your alpha blending logic(or option) in OpenGL.
Check your interpolation logic which is proportional to velocity of dragging.
It seems you don't have second one or not effective which is required to drawing app
I don't think the problem is in the texture but in the frame buffer to which you composite the line elements.
Your code fragments look like you draw segments by segment, so there are several overlapping segments drawn on top of each other. If the depth of the frame buffer is low there will be artifacts, especially in the lighter regions of the blended areas.
You can check the frame buffer using Xcode's OpenGL debugger. Activate it by running your code on the device and click the little "Capture OpenGL ES Frame" button: .
Select a "glBindFramebuffer" command in the "Debug Navigator" and look at the frame buffer description in the console area:
The interesting part is the GL_FRAMEBUFFER_INTERNAL_FORMAT.
In my opinion, the problem is in the blending mode you use when composing different image passes. I assume that you upload the texture for display only, and keep the in-memory image where you composite different drawing operations, or you read-back the image content using glReadPixels ?
Basically your second images appears like a straight-alpha image drawn like a pre-multiplied alpha image.
To be sure that it isn't a texture problem, save a NSImage to file before uploading to the texture, and check that the image is actually correct.
case 1:
I create the texture by
D3DXCreateTexture(device, width, height, 0, D3DUSAGE_DYNAMIC, D3DFMT_A8R8G8B8, D3DPOOL_DEFAULT, &texture)
and update the texture with white color.
D3DLOCKED_RECT lr;
HRESULT hr = texture->LockRect(0, &lr, NULL, 0);
ConvertRGB2RGBA(width, height, pixels, stride, (unsigned char*)(lr.pBits), lr.Pitch);
texture->UnlockRect(0);
the render result shows as:
What I want is pure white on the surface.
The z value of all the vertexes equals to 0.0f.
case 2:
If I create the texture by
D3DXCreateTextureFromFile(device, "e:\\test.bmp", &texture);
and do not update the texture, it shows absolutly correct.
case 3:
If I create the texture from file as case 2, and update the texture as case 1, the result is incorrect, there is test.bmp content remains slightly.
conclusion:
There must be something wrong with updating texture. What's wrong???
SOLVED!!!Change the levels param to 1, then it works.
D3DXCreateTexture(device, width, height, 1, D3DUSAGE_DYNAMIC, D3DFMT_A8R8G8B8, D3DPOOL_DEFAULT, &texture)
Congratulations. When the mipmap level argument of D3DXCreateTexture is set to 0, full mipmapped texture will be created. If you want to use mipmaps, your function ConvertRGB2RGBA should cover not only the top level texture, but also lower level textures.
Change the levels param to 1, then it works.
D3DXCreateTexture(device, width, height, 1, D3DUSAGE_DYNAMIC, D3DFMT_A8R8G8B8, D3DPOOL_DEFAULT, &texture)