I am using a simple shader, here it is
void main() {
vec2 p = -1.0 + 2.0 * v_tex_coord;
float len = length(p);
vec2 uv = v_tex_coord - (p/len)*(sin(len*22.-u_time*5.28) + 1.)*0.1;
gl_FragColor = texture2D(u_texture, uv) * u_color;
}
This is how I set it up to use it for nodes with different colors
self.swirlShader.attributes = [SKAttribute(name: "u_color", type: SKAttributeType.vectorFloat4)]
From time to time it glitches and adding nodes to the scene affects how it works, basically it changes the texture of the node to the sine function.
glitch example
This alternates between all nodes really fast, only when some particle is emitting, like the bottom-left one.
When 2 nodes collide they explode and when that happens it also crashes and the last instruction in the stack trace is [SKAttributeValue copyValueTo: type: count:]
Also getting this from time to time
Execution of the command buffer was aborted due to an error during execution. Caused GPU Hang Error (IOAF code 3)
EDIT: I found out that using a new instance of the shader for each node and increasing the number of nodes drastically increases the occurrence of the crash, but not the glitch, it actually changed it and made it less frequent. Here is the glitch with new instance for every node: glitch with new shader instances
UPDATE: It appears to be some kind of threading issue related to the access of the shader or the execution of the shader. Also, why is the CPU time going up and down when using a shader and steady low when not? I thought shaders work directly on the GPU.
UPDATE 2: Found out that it was crashing because I was adding too many nodes to the scene(around 3600). I don't know why though, because it isn't consistent and only happens when using a shader.
The glitch is still present and I can't figure out what exactly is causing it. I think it is again from adding nodes to the scene, but it is not consistent enough to run a lot of tests.
I tried removing all actions and doing manual alpha, rotation etc. updates, but that wasn't the cause. In one of the tests everything froze and started jumping back and forth between 2-3 frames, as well as jumping forward a few times, something is causing a GPU hang error.
I am not sure how the shader is being affected by anything outside it's variables, but it's messing with the GPU.
Working with Delphi / Firemonkey XE8. Had some decent luck with it recently, although you have to hack the heck out of it to get it to do what you want. My current project is to evaluate it's Low-Level 3D capabilities to see if I can use them as a starting point for a Game Project. I also know Unity3D quite well, and am considering using Unity3D instead, but I figure that Delphi / Firemonkey might give me some added flexibility in my game design because it is so minimal.
So I decided to dig into an Embarcadero-supplied sample... specifically the LowLevel3D sample. This is the cross-platform sample that shows you how to do nothing other than draw a rotating square on the screen with some custom shaders of your choice and have it look the same on all platforms (although it actually doesn't work AT ALL the same on all platforms... but we won't get into that).
Embc does not supply the original uncompiled shaders for the project (which I might add is really lame), and requires you to supply your own compatible shaders (some compiled, some not) for the various platforms you're targeting (also lame)...so my first job has been to create a shader that would work with their existing sample that does something OTHER than what the sample already does. Specifically, if I'm creating a 2D game, I wanted to make sure that I could do sprites with alpha transparency, basic stuff.... if I can get this working, I'll probably never have to write another shader for the whole game.
After pulling my hair out for many hours, I came up with this little shader that works with the same parameters as the demo.
Texture2D mytex0: register(t0);
Texture2D mytex1: register(t1);
float4 cccc : register(v0) ;
struct PixelShaderInput
{
float4 Pos: COLOR;
float2 Tex: TEXCOORDS;
};
SamplerState g_samLinear
{
Filter = MIN_MAG_MIP_LINEAR;
AddressU = Wrap;
AddressV = Wrap;
};
RasterizerState MyCull {
FrontCounterClockwise = FALSE;
};
float4 main(PixelShaderInput pIn): SV_TARGET
{
float4 cc,c;
float4 ci = mytex1.Sample(g_samLinear, pIn.Tex.xy);
c = ci;
c.a = 0;//<----- DOES NOT actually SET ALPHA TO ZERO ... THIS IS A PROBLEM
cc = c;
return cc;
}
Never-mind that it doesn't actually do much with the parameters, but check out the line where I set the output's ALPHA to 0. Well.... I found that this actually HAS NO EFFECT!
But it gets spookier than this. I found that turning on CULLING in the Delphi App FIXED this issue. So I figure... no big deal then, I'll just manually draw both sides of the sprite... right? Nope! When I manually drew a double sided sprite.. the problem came back!
Check this image: shader is ignoring alpha=0 when double-sided
In the above picture, clearly alpha is SOMEWHAT obeyed because the clouds are not surrounded by a black box, however, the cloud itself is super saturated (I find that if I multiply rgb*a, then the colors come out approximately right, but I'm not going to do that in real-life for obvious reasons.
I'm new to the concept of writing custom shaders. Any insight is appreciated.
I am trying to extract the color behind my shader fragment. I have searched around and found various examples of people doing this as such:
vec2 position = ( gl_FragCoord.xy / u_resolution.xy );
vec4 color = texture2D(u_backbuffer, v_texCoord);
This makes sense. However nobody has shown an example where you pass in the back buffer uniform.
I tried to do it like this:
int backbuffer = glGetUniformLocation(self.shaderProgram->program_, "u_backbuffer");
GLint textureID;
glGetIntegerv(GL_FRAMEBUFFER_BINDING, &textureID);//tried both of these one at a time
glGetIntegerv(GL_RENDERBUFFER_BINDING, &textureID);//tried both of these one at a time
glUniform1i(backbuffer, textureID);
But i just get black. This is in cocos2d iOS FYI
Any suggestions?
You can do this, but only on iOS 6.0. Apple added an extension called GL_EXT_shader_framebuffer_fetch which lets you read the contents of the current framebuffer at the fragment you're rendering. This extension introduces a new variable, called gl_lastFragData, which you can read in your fragment shader.
This question by RayDeeA shows en example of this in action, although you'll need to change the name of the extension as combinatorial points out in their answer.
This should be supported on all devices running iOS 6.0 and is a great way to implement custom blend modes. I've heard that it's a very low cost operation, but haven't done much profiling myself yet.
That is not allowed. You cannot simultaneously sample from an image that you're currently writing to as part of an FBO.
I'm using OpenTK in MonoTouch to render some textures in iOS, and some of the textures come up broken. This is a closeup of an iPad screenshot showing one correctly rendered texture (the top one) and two broken ones below:
I'm not doing anything weird. I'm loading the texture from a semitransparent PNG using CGImage->CGBitmapContext->GL.TexImage2D. I'm rendering each sprite with two triangles, and my fragment shader just reads the texel from the sampler with texture2D() and multiplies it by a uniform vec4 to color the texture.
The files themselves seem to be okay, and the Android port of the same application using Mono for Android, and the exact same binary resources renders them perfectly. As you can see, other transparent textures work fine.
If it helps, pretty much every texture is broken when I run the program in the simulator. Also this problem persists even if I rebuild the program.
Any ideas on how to figure out what is causing this problem?
Here's my vertex shader:
attribute vec4 spritePosition;
attribute vec2 textureCoords;
uniform mat4 projectionMatrix;
uniform vec4 color;
varying vec4 colorVarying;
varying vec2 textureVarying;
void main()
{
gl_Position = projectionMatrix * spritePosition;
textureVarying = textureCoords;
colorVarying = color;
}
Here's my fragment shader:
varying lowp vec4 colorVarying;
varying lowp vec2 textureVarying;
uniform sampler2D spriteTexture;
void main()
{
gl_FragColor = texture2D(spriteTexture, textureVarying) * colorVarying;
}
I'm loading the image like this:
using (var bitmap = UIImage.FromFile(resourcePath).CGImage)
{
IntPtr pixels = Marshal.AllocHGlobal(bitmap.Width * bitmap.Height * 4);
using (var context = new CGBitmapContext(pixels, bitmap.Width, bitmap.Height, 8, bitmap.Width * 4, bitmap.ColorSpace, CGImageAlphaInfo.PremultipliedLast))
{
context.DrawImage(new RectangleF(0, 0, bitmap.Width, bitmap.Height), bitmap);
int[] textureNames = new int[1];
GL.GenTextures(1, textureNames);
GL.BindTexture(TextureTarget.Texture2D, textureNames[0]);
GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMagFilter, (int)All.Linear);
GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMinFilter, (int)All.Linear);
GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureWrapS, (int)All.ClampToEdge);
GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureWrapT, (int)All.ClampToEdge);
GL.TexImage2D(TextureTarget.Texture2D, 0, PixelInternalFormat.Rgba, bitmap.Width, bitmap.Height, 0, PixelFormat.Rgba, PixelType.UnsignedByte, pixels);
CurrentResources.Add(resourceID, new ResourceData(resourcePath, resourceType, 0, new TextureEntry(textureNames[0], bitmap.Width, bitmap.Height)));
}
}
and in my onRenderFrame, I have this:
GL.ClearColor(1.0f, 1.0f, 1.0f, 1.0f);
GL.Clear(ClearBufferMask.ColorBufferBit);
GL.Enable(EnableCap.Blend);
GL.BlendFunc(BlendingFactorSrc.SrcAlpha, BlendingFactorDest.OneMinusSrcAlpha);
GL.UseProgram(RenderingProgram);
GL.VertexAttribPointer((int)ShaderAttributes.SpritePosition, 2, VertexAttribPointerType.Float, false, 0, squareVertices);
GL.VertexAttribPointer((int)ShaderAttributes.TextureCoords, 2, VertexAttribPointerType.Float, false, 0, squareTextureCoords);
GL.EnableVertexAttribArray((int)ShaderAttributes.SpritePosition);
GL.EnableVertexAttribArray((int)ShaderAttributes.TextureCoords);
//...
GL.ActiveTexture(TextureUnit.Texture0);
GL.BindTexture(TextureTarget.Texture2D, textureEntry.TextureID);
GL.Uniform1(Uniforms[(int)ShaderUniforms.Texture], 0);
// ...
GL.DrawArrays(BeginMode.TriangleStrip, 0, 4);
That triangle strip is made out of two triangles that make up the texture, with the vertex and texture coordinates set to where I want to show my sprite. projectionMatrix is a simple ortographic projection matrix.
As you can see, I'm not trying to do anything fancy here. This is all pretty standard code, and it works for some textures, so I think that in general the code is okay. I'm also doing pretty much the same thing in Mono for Android, and it works pretty well without any texture corruption.
Corrupted colors like that smell like uninitialized variables somewhere, and seeing it happen only on the transparent part leads me to believe that I'm having uninitialized alpha values somewhere. However, GL.Clear(ClearBufferMask.ColorBufferBit) should clear my alpha values, and even so, the background texture has an alpha value of 1, and with the current BlendFunc, should set the alpha for those pixels to 1. Afterwards, the transparent textures have alpha values ranging from 0 to 1, so they should blend properly. I see no uninitialized variables anywhere.
...or... this is all the fault of CGBitmapContext. Maybe by doing DrawImage, I'm not blitting the source image, but drawing it with blending instead, and the garbage data comes from when I did AllocGlobal. This doesn't explain why it consistently happens with just these two textures though... (I'm tagging this as core-graphics so maybe one of the quartz people can help)
Let me know if you want to see some more code.
Okay, it is just as I had expected. The memory I get with Marshal.AllocHGlobal is not initialized to anything, and CGBitmapContext.DrawImage just renders the image on top of whatever is in the context, which is garbage.
So the way to fix this is simply to insert a context.ClearRect() call before I call context.DrawImage().
I don't know why it worked fine with other (larger) textures, but maybe it is because in those cases, I'm requesting a large block of memory, so the iOS (or mono) memory manager gets a new zeroed block, while for the smaller textures, I'm reusing memory previously freed, which has not been zeroed.
It would be nice if your memory was allocated to something like 0xBAADF00D when using the debug heap, like LocalAlloc does in the Windows API.
Two other somewhat related things to remember:
In the code I posted, I'm not releasing the memory requested with AllocHGlobal. This is a bug. GL.TexImage2D copies the texture to VRAM, so it is safe to free it right there.
context.DrawImage is drawing the image into a new context (instead of reading the raw pixels from the image), and Core Graphics only works with premultiplied alpha (which I find idiotic). So the loaded texture will always be loaded with premultiplied alpha if I do it in this way. This means that I must also change the alpha blending function to GL.BlendFunc(BlendingFactorSrc.One, BlendingFactorDest.OneMinusSrcAlpha), and make sure that all crossfading code works over the entire RGBA, and not just the alpha value.
On iOS4 GL_OES_standard_derivatives is only supported on the device (from what I see when I output the extensions), is there a way to be able to:
Detect in the fragment shader if the extension is supported or not
If not supported, does anyone have a the code for the dFdx and dFdy? Can't seems that find anything on google.
TIA!
I had the same issue for antialiasing SDM fonts. You can calculate a similar dfdx/dfdx by
Translating 2 2d vectors using the current transform matrix :
vec2 p1(0,0); vec2 p2(1,1);
p1=TransformUsingCurrentMatrix(p1);
p2=TransformUsingCurrentMatrix(p2);
float magic=35; // you'll need to play with this - it's linked to screen size I think :P
float dFdx=(p2.x-p1.x)/magic;
float dFdy=(p2.y-p1.y)/magic;
then send dFdx/dFdy to your shader as uniforms - and simply multiply with your parameter to get the same functionality i.e.
dFdx(myval) now becomes
dFdx*myval;
dFdy(myval) dFdy*myval;
fwidth(myval) abs(dFdx*myval)+abs(dFdy*myval);