Sign in to follow this  
melbow

OpenGL 8 bit grayscale raw image problem

Recommended Posts

melbow    221
Hello, I am working on a terrain generator using heightmaps for a class I am currently in and I seem to have come across a problem which I cannot figure out, as I have very little experience using openGL. I have calculated a shadowmap based on my heightmap and saved it to my terrain file as simply a raw 8 bit image. However, when I attempt to load it into my graphics card I believe it thinks I am loading in a 24 bit image. I'm not sure so I will not speculate further, I'll just show you what is going on. When the shadow map is applied it looks like this: However, if I output the shadowmap as a .BMP it looks like it should, This is my shader source: Vertex Shader:
void main()
{
	gl_Position = gl_ProjectionMatrix*gl_ModelViewMatrix*gl_Vertex;
	gl_TexCoord[0] = gl_MultiTexCoord0;
}


Fragment shader:
uniform sampler2D sand;
uniform sampler2D grass;
uniform sampler2D rock;
uniform sampler2D snow;

uniform sampler2D shadowmap;
uniform sampler2D alphamap;

void main(void)
{
	vec4 shadow  = texture2D( shadowmap, gl_TexCoord[0].xy ).rgba;
	vec4 alpha   = texture2D( alphamap,  gl_TexCoord[0].xy ).rgba;
	
	vec4 tex0    = texture2D( sand,  gl_TexCoord[0].xy * 8.0 );
	vec4 tex1    = texture2D( grass, gl_TexCoord[0].xy * 8.0 );
	vec4 tex2    = texture2D( rock,  gl_TexCoord[0].xy * 8.0 );
	vec4 tex3    = texture2D( snow,  gl_TexCoord[0].xy * 8.0 );

	tex0 *= alpha.r;	// Red channel - sand/below sealevel
	tex1 = mix( tex0, tex1, alpha.g );	// Green channel - grass/above sealevel
	tex2 = mix( tex1, tex2, alpha.b );	// Blue channel - rock/steep slopes
	vec4 outColor = mix( tex2, tex3, alpha.a );	// Alpha channel - snow/high altitude
	outColor *= shadow;
	
	gl_FragColor = clamp( outColor, 0.0, 1.0 );
}


and this is how I load in the image:
		GLuint texture_id;

		glGenTextures(1, &texture_id);
		glBindTexture(GL_TEXTURE_2D, texture_id); 

		/* set texture parameters */
		if(GL_EXT_texture_filter_anisotropic)
		{
			float MaxAnisotropic;
			glGetFloatv(GL_MAX_TEXTURE_MAX_ANISOTROPY_EXT, &MaxAnisotropic);
			glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAX_ANISOTROPY_EXT, MaxAnisotropic);
		}

		// set parameters
		glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_NEAREST );
		glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
		glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT );
		glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT );

		// create mipmaps
		gluBuild2DMipmaps( GL_TEXTURE_2D, internal_format, width, height, format, type, data );


This is how I call it: GraphicsManager::GetSingleton().LoadRawTexture("shadowmap", 1, map->get_width(), map->get_height(), GL_LUMINANCE, GL_UNSIGNED_BYTE, map->get_shadowmap()); I use a hashmap in my graphics manager and hash the names of textures, that is why I have "shadowmap" as the 1st argument. That may be a bad way of doing it, I don't know, but I know that it works for what I am currently doing. So that isn't the issue here. All I do when I render is
		// set uniform for shadowmap
		sampler_loc = glGetUniformLocationARB(terrain_shader, "shadowmap");
		glActiveTextureARB(GL_TEXTURE4);
		GraphicsManager::GetSingleton().SetTexture("shadowmap");
		glUniform1iARB(sampler_loc, 4);


If it comes down to it I will store the image as RGB, just repeating the 8bit value, but as heightmaps can get large, that seems far from a good solution. [Edited by - melbow on May 1, 2009 10:14:46 AM]

Share this post


Link to post
Share on other sites
Digitalfragment    1504
GL_UNSIGNED_BYTE is making your glTexImage2D call expect 8 bits per pixel.

While its possible to use "GL_INTENSITY4" to indicate that the texture in video memory should be stored as 4-bit intensity, i believe that you still need to pass the data into glTexImage2D at a minimum of 8 bits per pixel (there is no type smaller than GL_UNSIGNED_BYTE)

so, when you load the file off disk, expand the data to 8-bits.

Something like this should do it: (off the top of my head, i may be wrong)


char * fourbitimage = whatever;
char * eightbitimage = malloc(numPixels);
for (int i = 0; i < numPixels/2; i++)
{
eightbitimage[i*2] = (fourbitimage[i] & 0x0F) << 1;
eightbitimage[i*2+1] = (fourbitimage[i] & 0xF0);
}
glTexImage2D(...whatever... GL_INTENSITTY4, GL_UNSIGNED_BYTE, eightbitimage);

Share this post


Link to post
Share on other sites
melbow    221
Quote:
Original post by Exorcist
GL_UNSIGNED_BYTE is making your glTexImage2D call expect 8 bits per pixel.


My goodness do I feel silly. I actually meant 8 bit. I've edited my post. Sorry, I've been awake for... let's just say way too long.

It is stored as Unsigned Bytes, and I write it to my file like this:

std::fstream out;
out.open(output_file, std::ios::out | std::ios::binary);
... //some code later
out.write((char *)t.lightmap, t.num_vertices()); //num vertices just does w*h

Share this post


Link to post
Share on other sites
Brother Bob    10344
The image you say is correct is 513x513, so you must check the padding and stride of the image. The default alignment, which is 4, is not divisible by the stride of the image, which appears to be 513 bytes. Either pad the image to 516 (the next multiple of 4 above 513) or set the unpack alignment to 1 (see glPixelStore).

Share this post


Link to post
Share on other sites
melbow    221
Ohhh! If I understand correctly then, that would explain why my RGBA raw loads just fine that is also 513x513.

Thank you very much.

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 ZeldaFan555
      Hello, My name is Matt. I am a programmer. I mostly use Java, but can use C++ and various other languages. I'm looking for someone to partner up with for random projects, preferably using OpenGL, though I'd be open to just about anything. If you're interested you can contact me on Skype or on here, thank you!
      Skype: Mangodoor408
    • By tyhender
      Hello, my name is Mark. I'm hobby programmer. 
      So recently,I thought that it's good idea to find people to create a full 3D engine. I'm looking for people experienced in scripting 3D shaders and implementing physics into engine(game)(we are going to use the React physics engine). 
      And,ye,no money =D I'm just looking for hobbyists that will be proud of their work. If engine(or game) will have financial succes,well,then maybe =D
      Sorry for late replies.
      I mostly give more information when people PM me,but this post is REALLY short,even for me =D
      So here's few more points:
      Engine will use openGL and SDL for graphics. It will use React3D physics library for physics simulation. Engine(most probably,atleast for the first part) won't have graphical fron-end,it will be a framework . I think final engine should be enough to set up an FPS in a couple of minutes. A bit about my self:
      I've been programming for 7 years total. I learned very slowly it as "secondary interesting thing" for like 3 years, but then began to script more seriously.  My primary language is C++,which we are going to use for the engine. Yes,I did 3D graphics with physics simulation before. No, my portfolio isn't very impressive. I'm working on that No,I wasn't employed officially. If anybody need to know more PM me. 
       
    • 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++.
      Question:
      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.
       
  • Popular Now