Sign in to follow this  

OpenGL Texture / Fog weirdness

Recommended Posts

kakum    123
I'm teaching myself OpenGL and trying to do some stuff with fog and texturing, and I've gotten some strange results. I'm using python, but the OpenGL bindings look about the same as C if that's what you're familiar with (minus semicolons and pointers, of course). Pictures speak louder than words, so here's what this code produces (called from glut idle callback function): glFogi(GL_FOG_MODE, GL_EXP) glFogfv(GL_FOG_COLOR, [.4, .3, .8, 1]) glFogf(GL_FOG_DENSITY, 0.35) glHint(GL_FOG_HINT, GL_DONT_CARE) glFogf(GL_FOG_START, 1.0) glFogf(GL_FOG_END, 5.0) glEnable(GL_FOG); Photobucket That GL_QUAD actually has a texture on it. The texture is generated using some code I borrowed from with some (I thought) minor modifications to read 24 bits instead of 32 (since no bitmaps I've come across have alpha components) and just use a straight up 2d array of RBGA arrays instead of the pygame Surface object. When I go to parse the pixels from this image: I get this as a result: Photobucket (Mind, I had to screencap that source image to get it into a bmp format proper for parsing, apparently standards aren't strictly enforced). Similarly, using this source image: Photobucket produces this as a result: Photobucket Note that the anime girl above was flipped vertically, but this one was not. I'm not sure what that could be attributed to. Also, the repeating color stripes on the L confuse me a bit, as though MSPaint does some odd form of compression or something that might create ill-effects, since even if it's the wrong color the entire L should be uniform. Here's the modified version of the pygame code I'm using to read the bitmap. f = open( filename, 'rb' ) data = f.close() # Assert: this is a Windows BMP if data[:2] != 'BM': raise Exception() pixel_data_offset = get_word( data[ 10:14 ] ) bitmap_info_header = data[ 14:(14+40) ] # Assert: this is a valid Windows BMP if get_word( bitmap_info_header[ :4 ] ) != 40: raise Exception() # Assert: image type is BI_RGB (not compressed) if get_word( bitmap_info_header[ 16:20 ] ) != 0: raise Exception() width = get_word( bitmap_info_header[ 4:8 ] ) height = get_word( bitmap_info_header[ 8:12 ] ) bitcount = get_word( bitmap_info_header[ 14:16 ] ) # Assert: bitmap has bitdepth of 32-bits per pixel if bitcount != 24: raise Exception() is_inverted = (height < 0) if is_inverted: height = -height # Load and store the image data .......................................... result = list() try: for y in xrange( height ): result.append(list()) for x in xrange( width ): result[y].append(list()) result[y][x].append( [ord( data[ pixel_data_offset + 1 ] ), # Red ord( data[ pixel_data_offset + 0 ] ), # Green ord( data[ pixel_data_offset + 2 ] ), # Blue 0] # Alpha ) pixel_data_offset += 3 To display the texture in the display callback I'm using: glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST) glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST) glTexImage2D ( GL_TEXTURE_2D, 0, GL_RGBA, 50, 50, 0, GL_RGBA, GL_UNSIGNED_BYTE, test) glEnable( GL_TEXTURE_2D ) glBegin( GL_QUADS ) glTexCoord2f ( 0.0, 0.0 ) glVertex3f( 0, 0, -100 ) glTexCoord2f( 1.0, 0.0 ) glVertex3f( 50, 0, -100 ) glTexCoord2f( 1.0, 1.0 ) glVertex3f( 50, 50, -100 ) glTexCoord2f( 0.0, 1.0 ) glVertex3f( 0, 50, -100 ) glEnd() glDisable( GL_TEXTURE_2D ) This seems straightforward enough that I don't think there's an issue there. Feel free to cry RTFM, but please point me to TFM, since that pygame link is all I've found on reading RGB data from bitmaps, and they aren't the greatest at documentation. <tangent> Also, what's the html tag for a scroll box for code? Also also, being able to preserve my tabs so that python code is understandable would be nice >_> </tangent>

Share this post

Link to post
Share on other sites
zedz    291
from the pictures it looks like youre loading the textures incorrectly

using windows bitmaps ie *.bmp are usually 24bits perpixel ie GL_RGB but u have
glTexImage2D ( GL_TEXTURE_2D, 0, GL_RGBA, 50, 50, 0, GL_RGBA, GL_UNSIGNED_BYTE, test)


glTexImage2D ( GL_TEXTURE_2D, 0, GL_RGB8, 50, 50, 0, GL_RGB, GL_UNSIGNED_BYTE, test)

Share this post

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this  

  • Similar Content

    • By Zaphyk
      I am developing my engine using the OpenGL 3.3 compatibility profile. It runs as expected on my NVIDIA card and on my Intel Card however when I tried it on an AMD setup it ran 3 times worse than on the other setups. Could this be a AMD driver thing or is this probably a problem with my OGL code? Could a different code standard create such bad performance?
    • By Kjell Andersson
      I'm trying to get some legacy OpenGL code to run with a shader pipeline,
      The legacy code uses glVertexPointer(), glColorPointer(), glNormalPointer() and glTexCoordPointer() to supply the vertex information.
      I know that it should be using setVertexAttribPointer() etc to clearly define the layout but that is not an option right now since the legacy code can't be modified to that extent.
      I've got a version 330 vertex shader to somewhat work:
      #version 330 uniform mat4 osg_ModelViewProjectionMatrix; uniform mat4 osg_ModelViewMatrix; layout(location = 0) in vec4 Vertex; layout(location = 2) in vec4 Normal; // Velocity layout(location = 3) in vec3 TexCoord; // TODO: is this the right layout location? out VertexData { vec4 color; vec3 velocity; float size; } VertexOut; void main(void) { vec4 p0 = Vertex; vec4 p1 = Vertex + vec4(Normal.x, Normal.y, Normal.z, 0.0f); vec3 velocity = (osg_ModelViewProjectionMatrix * p1 - osg_ModelViewProjectionMatrix * p0).xyz; VertexOut.velocity = velocity; VertexOut.size = TexCoord.y; gl_Position = osg_ModelViewMatrix * Vertex; } What works is the Vertex and Normal information that the legacy C++ OpenGL code seem to provide in layout location 0 and 2. This is fine.
      What I'm not getting to work is the TexCoord information that is supplied by a glTexCoordPointer() call in C++.
      What layout location is the old standard pipeline using for glTexCoordPointer()? Or is this undefined?
      Side note: I'm trying to get an OpenSceneGraph 3.4.0 particle system to use custom vertex, geometry and fragment shaders for rendering the particles.
    • By markshaw001
      Hi i am new to this forum  i wanted to ask for help from all of you i want to generate real time terrain using a 32 bit heightmap i am good at c++ and have started learning Opengl as i am very interested in making landscapes in opengl i have looked around the internet for help about this topic but i am not getting the hang of the concepts and what they are doing can some here suggests me some good resources for making terrain engine please for example like tutorials,books etc so that i can understand the whole concept of terrain generation.
    • By KarimIO
      Hey guys. I'm trying to get my application to work on my Nvidia GTX 970 desktop. It currently works on my Intel HD 3000 laptop, but on the desktop, every bind textures specifically from framebuffers, I get half a second of lag. This is done 4 times as I have three RGBA textures and one depth 32F buffer. I tried to use debugging software for the first time - RenderDoc only shows SwapBuffers() and no OGL calls, while Nvidia Nsight crashes upon execution, so neither are helpful. Without binding it runs regularly. This does not happen with non-framebuffer binds.
      GLFramebuffer::GLFramebuffer(FramebufferCreateInfo createInfo) { glGenFramebuffers(1, &fbo); glBindFramebuffer(GL_FRAMEBUFFER, fbo); textures = new GLuint[createInfo.numColorTargets]; glGenTextures(createInfo.numColorTargets, textures); GLenum *DrawBuffers = new GLenum[createInfo.numColorTargets]; for (uint32_t i = 0; i < createInfo.numColorTargets; i++) { glBindTexture(GL_TEXTURE_2D, textures[i]); GLint internalFormat; GLenum format; TranslateFormats(createInfo.colorFormats[i], format, internalFormat); // returns GL_RGBA and GL_RGBA glTexImage2D(GL_TEXTURE_2D, 0, internalFormat, createInfo.width, createInfo.height, 0, format, GL_FLOAT, 0); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); DrawBuffers[i] = GL_COLOR_ATTACHMENT0 + i; glBindTexture(GL_TEXTURE_2D, 0); glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0 + i, textures[i], 0); } if (createInfo.depthFormat != FORMAT_DEPTH_NONE) { GLenum depthFormat; switch (createInfo.depthFormat) { case FORMAT_DEPTH_16: depthFormat = GL_DEPTH_COMPONENT16; break; case FORMAT_DEPTH_24: depthFormat = GL_DEPTH_COMPONENT24; break; case FORMAT_DEPTH_32: depthFormat = GL_DEPTH_COMPONENT32; break; case FORMAT_DEPTH_24_STENCIL_8: depthFormat = GL_DEPTH24_STENCIL8; break; case FORMAT_DEPTH_32_STENCIL_8: depthFormat = GL_DEPTH32F_STENCIL8; break; } glGenTextures(1, &depthrenderbuffer); glBindTexture(GL_TEXTURE_2D, depthrenderbuffer); glTexImage2D(GL_TEXTURE_2D, 0, depthFormat, createInfo.width, createInfo.height, 0, GL_DEPTH_COMPONENT, GL_FLOAT, 0); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); glBindTexture(GL_TEXTURE_2D, 0); glFramebufferTexture(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, depthrenderbuffer, 0); } if (createInfo.numColorTargets > 0) glDrawBuffers(createInfo.numColorTargets, DrawBuffers); else glDrawBuffer(GL_NONE); if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) std::cout << "Framebuffer Incomplete\n"; glBindFramebuffer(GL_FRAMEBUFFER, 0); width = createInfo.width; height = createInfo.height; } // ... // FBO Creation FramebufferCreateInfo gbufferCI; gbufferCI.colorFormats =; gbufferCI.depthFormat = FORMAT_DEPTH_32; gbufferCI.numColorTargets = gbufferCFs.size(); gbufferCI.width = engine.settings.resolutionX; gbufferCI.height = engine.settings.resolutionY; gbufferCI.renderPass = nullptr; gbuffer = graphicsWrapper->CreateFramebuffer(gbufferCI); // Bind glBindFramebuffer(GL_DRAW_FRAMEBUFFER, fbo); // Draw here... // Bind to textures glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, textures[0]); glActiveTexture(GL_TEXTURE1); glBindTexture(GL_TEXTURE_2D, textures[1]); glActiveTexture(GL_TEXTURE2); glBindTexture(GL_TEXTURE_2D, textures[2]); glActiveTexture(GL_TEXTURE3); glBindTexture(GL_TEXTURE_2D, depthrenderbuffer); Here is an extract of my code. I can't think of anything else to include. I've really been butting my head into a wall trying to think of a reason but I can think of none and all my research yields nothing. Thanks in advance!
    • By Adrianensis
      Hi everyone, I've shared my 2D Game Engine source code. It's the result of 4 years working on it (and I still continue improving features ) and I want to share with the community. You can see some videos on youtube and some demo gifs on my twitter account.
      This Engine has been developed as End-of-Degree Project and it is coded in Javascript, WebGL and GLSL. The engine is written from scratch.
      This is not a professional engine but it's for learning purposes, so anyone can review the code an learn basis about graphics, physics or game engine architecture. Source code on this GitHub repository.
      I'm available for a good conversation about Game Engine / Graphics Programming
  • Popular Now