Followers 0

# OpenGL [ES 2.0] Texture rendering problem

## 3 posts in this topic

Hi everyone,

Recently I've been working on a page curl effect in Opengl ES 2.0 for embedded systems. I've been able to write the model and surface deformation algorithm properly, but I have problems with rendering it with a texture. I have attached three screenshots showing exactly the problem I get when rendering the curl at certain angles of the deformation cylinder (yes, the page is deformed around a cylinder). The problem is that if the angle of the cylinder is higher than PI / 2 the texture renders all perfectly, but if it's smaller I get some transparent stripes which you can see through and if you make the angle even smaller the whole bended surface seems to be transparent for the page behind.

I have checked if it's not a problem of the mathematical model (the surface crossing itself), but it's not. I have also disabled face culling and alpha blending in this case and I'm out of ideas what can be wrong. I would be very grateful if somebody gave me a hint where to start from.

The vertex shader I use is very simple:

uniform mat4 uPositionMatrix;
uniform mat4 uMV;

attribute vec4 aPosition;
attribute vec2 aTextureCoord;

varying vec4 vTextureCoord;

void main()
{
vTextureCoord = aTextureCoord;
gl_Position = uPositionMatrix * aPosition;
}


// Fragment shader program
precision highp float;

varying vec2 vTextureCoord;

uniform sampler2D sTexture;

void main (void)
{
gl_FragColor =  texture2D(sTexture, vTextureCoord);
}


I know I didn't give you a lot of details, but as I don't know where to start from I'll wait for any questions for more details.

[attachment=17955:Screen-20130920154606519612.jpg]

[attachment=17956:Screen-20130920154613617023.jpg]

[attachment=17957:Screen-20130920154618177095.jpg]

0

##### Share on other sites

Looks like z-fighting. The curling part of the page (on the cylinder, as you say) looks like it's actually partially intersecting the flat part of the page - make sure your depth buffer is properly setup.

2

##### Share on other sites

Looks like z-fighting. The curling part of the page (on the cylinder, as you say) looks like it's actually partially intersecting the flat part of the page - make sure your depth buffer is properly setup.

If I understand it properly z-fighting takes place whenever the z values of the vertices are very close, but in my case the weird thing is that they are very well separated. Please explain me this if I'm wrong.

As per the depth test I call:

glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_LEQUAL);

The EGL initialization is as follows:

EGLint numConfigs = 1;
EGLint eglConfigList[] =
{ EGL_RED_SIZE, 8, EGL_GREEN_SIZE, 8, EGL_BLUE_SIZE, 8, EGL_ALPHA_SIZE, 0, EGL_DEPTH_SIZE, 8, EGL_SURFACE_TYPE,
EGL_WINDOW_BIT, EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT, EGL_NONE } ;

EGLint eglContextList[] =
{ EGL_CONTEXT_CLIENT_VERSION, 2, EGL_NONE } ;

eglBindAPI(EGL_OPENGL_ES_API);
m_Display = eglGetDisplay((EGLNativeDisplayType)EGL_DEFAULT_DISPLAY);
if (m_Display == EGL_NO_DISPLAY)
return -1;

if (eglInitialize(m_Display, null, null) != EGL_TRUE)
return -1;

if (eglChooseConfig(m_Display, eglConfigList, &m_eglConfig, 1, &numConfigs) != EGL_TRUE)
return -1;

if ((m_eglSurface = eglCreateWindowSurface(m_Display, m_eglConfig, (EGLNativeWindowType)m_pForm, null)) == EGL_NO_SURFACE)
return -1;

if ((m_eglContext = eglCreateContext(m_Display, m_eglConfig, EGL_NO_CONTEXT, eglContextList)) == EGL_NO_CONTEXT)
return -1;

if (eglMakeCurrent(m_Display, m_eglSurface, m_eglSurface, m_eglContext) != EGL_TRUE)
return -1;

return 0;


Shouldn't this be enough?

0

##### Share on other sites

For posterity, I found the problem. It was in the frustum setup. I have set the near plane to 0.001f and far to 10000.0f which caused some rounding errors probably. Changing the near plane to 10.0f eliminated the  problem.

Thanks!

0

## Create an account

Register a new account

Followers 0

• ### Similar Content

• So it's been a while since I took a break from my whole creating a planet in DX11. Last time around I got stuck on fixing a nice LOD.
A week back or so I got help to find this:
https://github.com/sp4cerat/Planet-LOD
In general this is what I'm trying to recreate in DX11, he that made that planet LOD uses OpenGL but that is a minor issue and something I can solve. But I have a question regarding the code
He gets the position using this row
vec4d pos = b.var.vec4d["position"]; Which is then used further down when he sends the variable "center" into the drawing function:
if (pos.len() < 1) pos.norm(); world::draw(vec3d(pos.x, pos.y, pos.z));
Inside the draw function this happens:
draw_recursive(p3[0], p3[1], p3[2], center); Basically the 3 vertices of the triangle and the center of details that he sent as a parameter earlier: vec3d(pos.x, pos.y, pos.z)
Now onto my real question, he does vec3d edge_center[3] = { (p1 + p2) / 2, (p2 + p3) / 2, (p3 + p1) / 2 }; to get the edge center of each edge, nothing weird there.
But this is used later on with:
vec3d d = center + edge_center[i]; edge_test[i] = d.len() > ratio_size; edge_test is then used to evaluate if there should be a triangle drawn or if it should be split up into 3 new triangles instead. Why is it working for him? shouldn't it be like center - edge_center or something like that? Why adding them togheter? I asume here that the center is the center of details for the LOD. the position of the camera if stood on the ground of the planet and not up int he air like it is now.

Full code can be seen here:
https://github.com/sp4cerat/Planet-LOD/blob/master/src.simple/Main.cpp
If anyone would like to take a look and try to help me understand this code I would love this person. I'm running out of ideas on how to solve this in my own head, most likely twisted it one time to many up in my head
Toastmastern

• I googled around but are unable to find source code or details of implementation.
What keywords should I search for this topic?
Things I would like to know:
A. How to ensure that partially covered pixels are rasterized?
Apparently by expanding each triangle by 1 pixel or so, rasterization problem is almost solved.
But it will result in an unindexable triangle list without tons of overlaps. Will it incur a large performance penalty?
How to ensure proper synchronizations in GLSL?
GLSL seems to only allow int32 atomics on image.
C. Is there some simple ways to estimate coverage on-the-fly?
In case I am to draw 2D shapes onto an exisitng target:
1. A multi-pass whatever-buffer seems overkill.
2. Multisampling could cost a lot memory though all I need is better coverage.
Besides, I have to blit twice, if draw target is not multisampled.

• By mapra99
Hello

I am working on a recent project and I have been learning how to code in C# using OpenGL libraries for some graphics. I have achieved some quite interesting things using TAO Framework writing in Console Applications, creating a GLUT Window. But my problem now is that I need to incorporate the Graphics in a Windows Form so I can relate the objects that I render with some .NET Controls.

To deal with this problem, I have seen in some forums that it's better to use OpenTK instead of TAO Framework, so I can use the glControl that OpenTK libraries offer. However, I haven't found complete articles, tutorials or source codes that help using the glControl or that may insert me into de OpenTK functions. Would somebody please share in this forum some links or files where I can find good documentation about this topic? Or may I use another library different of OpenTK?

Thanks!

• Hello, I have been working on SH Irradiance map rendering, and I have been using a GLSL pixel shader to render SH irradiance to 2D irradiance maps for my static objects. I already have it working with 9 3D textures so far for the first 9 SH functions.
In my GLSL shader, I have to send in 9 SH Coefficient 3D Texures that use RGBA8 as a pixel format. RGB being used for the coefficients for red, green, and blue, and the A for checking if the voxel is in use (for the 3D texture solidification shader to prevent bleeding).
My problem is, I want to knock this number of textures down to something like 4 or 5. Getting even lower would be a godsend. This is because I eventually plan on adding more SH Coefficient 3D Textures for other parts of the game map (such as inside rooms, as opposed to the outside), to circumvent irradiance probe bleeding between rooms separated by walls. I don't want to reach the 32 texture limit too soon. Also, I figure that it would be a LOT faster.
Is there a way I could, say, store 2 sets of SH Coefficients for 2 SH functions inside a texture with RGBA16 pixels? If so, how would I extract them from inside GLSL? Let me know if you have any suggestions ^^.
• By KarimIO
EDIT: I thought this was restricted to Attribute-Created GL contexts, but it isn't, so I rewrote the post.
Hey guys, whenever I call SwapBuffers(hDC), I get a crash, and I get a "Too many posts were made to a semaphore." from Windows as I call SwapBuffers. What could be the cause of this?
Update: No crash occurs if I don't draw, just clear and swap.
static PIXELFORMATDESCRIPTOR pfd = // pfd Tells Windows How We Want Things To Be { sizeof(PIXELFORMATDESCRIPTOR), // Size Of This Pixel Format Descriptor 1, // Version Number PFD_DRAW_TO_WINDOW | // Format Must Support Window PFD_SUPPORT_OPENGL | // Format Must Support OpenGL PFD_DOUBLEBUFFER, // Must Support Double Buffering PFD_TYPE_RGBA, // Request An RGBA Format 32, // Select Our Color Depth 0, 0, 0, 0, 0, 0, // Color Bits Ignored 0, // No Alpha Buffer 0, // Shift Bit Ignored 0, // No Accumulation Buffer 0, 0, 0, 0, // Accumulation Bits Ignored 24, // 24Bit Z-Buffer (Depth Buffer) 0, // No Stencil Buffer 0, // No Auxiliary Buffer PFD_MAIN_PLANE, // Main Drawing Layer 0, // Reserved 0, 0, 0 // Layer Masks Ignored }; if (!(hDC = GetDC(windowHandle))) return false; unsigned int PixelFormat; if (!(PixelFormat = ChoosePixelFormat(hDC, &pfd))) return false; if (!SetPixelFormat(hDC, PixelFormat, &pfd)) return false; hRC = wglCreateContext(hDC); if (!hRC) { std::cout << "wglCreateContext Failed!\n"; return false; } if (wglMakeCurrent(hDC, hRC) == NULL) { std::cout << "Make Context Current Second Failed!\n"; return false; } ... // OGL Buffer Initialization glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT); glBindVertexArray(vao); glUseProgram(myprogram); glDrawElements(GL_TRIANGLES, indexCount, GL_UNSIGNED_SHORT, (void *)indexStart); SwapBuffers(GetDC(window_handle));

• 22
• 11
• 15
• 17
• 19