• Advertisement

Archived

This topic is now archived and is closed to further replies.

OpenGL OpenGL & 2d - Example given does not work, any ideas ?

This topic is 5589 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

Hi, I have kept quiet for a week or 2 now, and think I have learnt a fair amount of the basic stuff I need to know. Now, I am stuck again, and it has to be something really simple, probably a case of not seeing the wood for the trees ! I am trying to set up my drawing area for a coordinate based system that I can relate to (i.e. 640 * 480), and not just the seemingly abitrary opengl units. (I got teh example from someone on heres source code, just to see how it was done) My code below however does not work, when I think it should. I even copied someone elses code that does work using a similar method, and can''t get that to work either. Here is my initialisation function.
  

	PIXELFORMATDESCRIPTOR pfd;
    int         n;
	HGLRC		hrc;
	GLfloat     fMaxObjSize, fAspect;
	GLfloat     fNearPlane, fFarPlane;

    ASSERT(m_pDC != NULL);

    if (!bSetupPixelFormat(m_pDC))
        return;

// Interrogates the Pixel Format to see if a Palette is needed.

    n = ::GetPixelFormat(m_pDC->GetSafeHdc());
    ::DescribePixelFormat(m_pDC->GetSafeHdc(), n, sizeof(pfd), &pfd);

//If a Palette is needeed, then create one.(256 Colours Only)

//Detect if Needed by Anding the Value in the Data flags and the Need Palette Flag

	if ((pfd.dwFlags & PFD_NEED_PALETTE)) 
	{
								
		CreateRGBPalette(m_pDC);
	}
	
    // create a rendering context and make it current

        
    hrc = wglCreateContext(m_pDC->GetSafeHdc());
    wglMakeCurrent(m_pDC->GetSafeHdc(), hrc);

	//Clear the Depth Buffer

    glClearDepth(1.0f);
	//Enable OGL using the Depth Buffer for comparisons

    glEnable(GL_DEPTH_TEST);


//Initialise OpenGL for 2d


	glViewport(0,0,640,480);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glOrtho(0.0f,640.0f,0.0f,480.0f,-10.0f,10.0f);
	
	glMatrixMode(GL_MODELVIEW);

	glShadeModel(GL_SMOOTH);							
	glClearColor(0.0f, 0.0f, 0.0f, 0.5f);			
	glClearDepth(1.0f);									
	glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);	
	glEnable(GL_TEXTURE_2D);

	//Select the GL Projection Matrix (Stack)

    glMatrixMode(GL_PROJECTION);
	//Reset Identity Matrix

    glLoadIdentity();	
	
}
  
and my draw scene function...
  
int CMyOgl::DrawGLScene()
{
	
    static BOOL     bBusy = FALSE;	
	if(bBusy)
        return TRUE;

    bBusy = TRUE;

	//Setup Drawing Area Back Colour

	glClearColor(m_BackColour.fRed, m_BackColour.fGreen, m_BackColour.fBlue, m_BackColour.fAlpha);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
	//Reset the Drawing Point to the Centre of the screen

	glLoadIdentity();	
	

  glColor3f(0.5f,0.5f,0.5f);
	glBegin(GL_LINES);
		glVertex3f(160.0f,120.0f,0.0f);
		glVertex3f(480.0f,120.0f,0.0f);

		glVertex3f(480.0f,120.0f,0.0f);
		glVertex3f(480.0f,360.0f,0.0f);

		glVertex3f(480.0f,360.0f,0.0f);
		glVertex3f(160.0f,360.0f,0.0f);

		glVertex3f(160.0f,360.0f,0.0f);
		glVertex3f(160.0f,120.0f,0.0f);
	glEnd();
	
	
	
	SwapBuffers(wglGetCurrentDC());

    bBusy = FALSE;
	
	glFlush();	

	return TRUE;
}
  
If anyone can offer me any hints or even fix my probelm I''ll be very greatful. As an aside, if I set my system up in this manner and draw in teh z plane at 0, is there an easy way of finding out how the coordinates I have set will change if I draw in another z plane, or have I misunderstood something fundamental ? TYVMIA, Bp.

Share this post


Link to post
Share on other sites
Advertisement
Guest Anonymous Poster
at least part of your mistake is in your initialization.

you setup a nice viewport and projection.
then you setup some model view stuff.

then you clobber your projection!

<code>
glClearDepth(1.0f);
//Enable OGL using the Depth Buffer for comparisons
glEnable(GL_DEPTH_TEST);
//Initialise OpenGL for 2d
glViewport(0,0,640,480);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0.0f,640.0f,0.0f,480.0f,-10.0f,10.0f);

glMatrixMode(GL_MODELVIEW);
glShadeModel(GL_SMOOTH);
glClearColor(0.0f, 0.0f, 0.0f, 0.5f);
glClearDepth(1.0f); // note -- you already did this.
glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);
glEnable(GL_TEXTURE_2D);

//Select the GL Projection Matrix (Stack)
glMatrixMode(GL_PROJECTION);
//Reset Identity Matrix -- clobbers projection!
glLoadIdentity();

</code>

i don''t know why you''re selecting the projection matrix at the end. after you''ve initialized, everything you do will be (probably) in the modelview matrix.

step 1) don''t clobber your projection matrix.

another note. depending on whether you use single or double buffering, you maybe should call glFlush() before the SwapBuffers. it makes more sense that way.

i''m not a windows guy, really, so i don''t know if you''re doing it on purpose. (calling glFlush after SwapBuffers) but in general i don''t think it makes sense. you may need it before Swap, though, to get your card to actually draw (since you''re using just a few vertices.)

thanks,
ryan.

Share this post


Link to post
Share on other sites
Thanks Ryan, I Have fixed those, but I still get a white screen with no lines on it. Any more takers ?

Bp.

Share this post


Link to post
Share on other sites
OK, so following Ap''s comment, I now have the following...


  
PIXELFORMATDESCRIPTOR pfd;
int n;
HGLRC hrc;

ASSERT(m_pDC != NULL);

if (!bSetupPixelFormat(m_pDC))
return;

// Interrogates the Pixel Format to see if a Palette is needed.

n = ::GetPixelFormat(m_pDC->GetSafeHdc());
::DescribePixelFormat(m_pDC->GetSafeHdc(), n, sizeof(pfd), &pfd);

//If a Palette is needeed, then create one.(256 Colours Only)

//Detect if Needed by Anding the Value in the Data flags and the Need Palette Flag

if ((pfd.dwFlags & PFD_NEED_PALETTE))
{

CreateRGBPalette(m_pDC);
}

// create a rendering context and make it current


hrc = wglCreateContext(m_pDC->GetSafeHdc());
wglMakeCurrent(m_pDC->GetSafeHdc(), hrc);

//Enable OGL using the Depth Buffer for comparisons

glEnable(GL_DEPTH_TEST);

//Initialise OpenGL for 2d


glViewport(0,0,640,480);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0.0f,640.0f,0.0f,480.0f,-10.0f,10.0f);

glMatrixMode(GL_MODELVIEW);
glShadeModel(GL_SMOOTH);
glClearColor(0.0f, 0.0f, 0.0f, 0.5f);
glClearDepth(1.0f);
glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);
glEnable(GL_TEXTURE_2D);

//Select the GL Projection Matrix (Stack)


glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// glLoadIdentity();


//Set up the viewing angle

// gluPerspective(0.0f, fAspect, fNearPlane, fFarPlane); //Setup Perspective Matrix


//Initialise Matrix Mode

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

///Temporary code


// glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);


glColor3f(1.0f, 0.0f, 0.0f);

glBegin(GL_LINES);
glVertex3f(160.0f,120.0f,0.0f);
glVertex3f(480.0f,120.0f,0.0f);

glVertex3f(480.0f,120.0f,0.0f);
glVertex3f(480.0f,360.0f,0.0f);

glVertex3f(480.0f,360.0f,0.0f);
glVertex3f(160.0f,360.0f,0.0f);

glVertex3f(160.0f,360.0f,0.0f);
glVertex3f(160.0f,120.0f,0.0f);

glEnd();

glFlush();

SwapBuffers(wglGetCurrentDC());


And still just the white screen, no lines.

This is driving me nuts, it has to be obvious, so what am I missing ?

TIA,

Bp.

Share this post


Link to post
Share on other sites
Not certain about this .. but try drawing the lines at a +ve Z coord, rather than 0.

glBegin(GL_LINES);
glVertex3f(160.0f,120.0f,5.0 f);
glVertex3f(480.0f,120.0f,5.0 f);
glVertex3f(480.0f,120.0f,5.0 f);
glVertex3f(480.0f,360.0f,5.0 f);
glVertex3f(480.0f,360.0f,5.0 f);
glVertex3f(160.0f,360.0f,5.0 f);
glVertex3f(160.0f,360.0f,5.0 f);
glVertex3f(160.0f,120.0f,5.0 f);
glEnd();

I think the problem is that the camera is at Z=0 and so are the lines, so nothing gets drawn.

Not 100% certain, tho, so E&OE

Edit: Ignore me. I had a play around with some glOrtho stuff and anything within Z=-10 -> Z=10 should get drawn fine. sorry for being no help

[edited by - SimbobX on October 1, 2002 7:21:51 AM]

Share this post


Link to post
Share on other sites

  • Advertisement
  • Advertisement
  • Popular Now

  • Advertisement
  • Similar Content

    • By Balma Alparisi
      i got error 1282 in my code.
      sf::ContextSettings settings; settings.majorVersion = 4; settings.minorVersion = 5; settings.attributeFlags = settings.Core; sf::Window window; window.create(sf::VideoMode(1600, 900), "Texture Unit Rectangle", sf::Style::Close, settings); window.setActive(true); window.setVerticalSyncEnabled(true); glewInit(); GLuint shaderProgram = createShaderProgram("FX/Rectangle.vss", "FX/Rectangle.fss"); float vertex[] = { -0.5f,0.5f,0.0f, 0.0f,0.0f, -0.5f,-0.5f,0.0f, 0.0f,1.0f, 0.5f,0.5f,0.0f, 1.0f,0.0f, 0.5,-0.5f,0.0f, 1.0f,1.0f, }; GLuint indices[] = { 0,1,2, 1,2,3, }; GLuint vao; glGenVertexArrays(1, &vao); glBindVertexArray(vao); GLuint vbo; glGenBuffers(1, &vbo); glBindBuffer(GL_ARRAY_BUFFER, vbo); glBufferData(GL_ARRAY_BUFFER, sizeof(vertex), vertex, GL_STATIC_DRAW); GLuint ebo; glGenBuffers(1, &ebo); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo); glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices,GL_STATIC_DRAW); glVertexAttribPointer(0, 3, GL_FLOAT, false, sizeof(float) * 5, (void*)0); glEnableVertexAttribArray(0); glVertexAttribPointer(1, 2, GL_FLOAT, false, sizeof(float) * 5, (void*)(sizeof(float) * 3)); glEnableVertexAttribArray(1); GLuint texture[2]; glGenTextures(2, texture); glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, texture[0]); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); sf::Image* imageOne = new sf::Image; bool isImageOneLoaded = imageOne->loadFromFile("Texture/container.jpg"); if (isImageOneLoaded) { glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, imageOne->getSize().x, imageOne->getSize().y, 0, GL_RGBA, GL_UNSIGNED_BYTE, imageOne->getPixelsPtr()); glGenerateMipmap(GL_TEXTURE_2D); } delete imageOne; glActiveTexture(GL_TEXTURE1); glBindTexture(GL_TEXTURE_2D, texture[1]); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); sf::Image* imageTwo = new sf::Image; bool isImageTwoLoaded = imageTwo->loadFromFile("Texture/awesomeface.png"); if (isImageTwoLoaded) { glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, imageTwo->getSize().x, imageTwo->getSize().y, 0, GL_RGBA, GL_UNSIGNED_BYTE, imageTwo->getPixelsPtr()); glGenerateMipmap(GL_TEXTURE_2D); } delete imageTwo; glUniform1i(glGetUniformLocation(shaderProgram, "inTextureOne"), 0); glUniform1i(glGetUniformLocation(shaderProgram, "inTextureTwo"), 1); GLenum error = glGetError(); std::cout << error << std::endl; sf::Event event; bool isRunning = true; while (isRunning) { while (window.pollEvent(event)) { if (event.type == event.Closed) { isRunning = false; } } glClear(GL_COLOR_BUFFER_BIT); if (isImageOneLoaded && isImageTwoLoaded) { glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, texture[0]); glActiveTexture(GL_TEXTURE1); glBindTexture(GL_TEXTURE_2D, texture[1]); glUseProgram(shaderProgram); } glBindVertexArray(vao); glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, nullptr); glBindVertexArray(0); window.display(); } glDeleteVertexArrays(1, &vao); glDeleteBuffers(1, &vbo); glDeleteBuffers(1, &ebo); glDeleteProgram(shaderProgram); glDeleteTextures(2,texture); return 0; } and this is the vertex shader
      #version 450 core layout(location=0) in vec3 inPos; layout(location=1) in vec2 inTexCoord; out vec2 TexCoord; void main() { gl_Position=vec4(inPos,1.0); TexCoord=inTexCoord; } and the fragment shader
      #version 450 core in vec2 TexCoord; uniform sampler2D inTextureOne; uniform sampler2D inTextureTwo; out vec4 FragmentColor; void main() { FragmentColor=mix(texture(inTextureOne,TexCoord),texture(inTextureTwo,TexCoord),0.2); } I was expecting awesomeface.png on top of container.jpg

    • By khawk
      We've just released all of the source code for the NeHe OpenGL lessons on our Github page at https://github.com/gamedev-net/nehe-opengl. code - 43 total platforms, configurations, and languages are included.
      Now operated by GameDev.net, NeHe is located at http://nehe.gamedev.net where it has been a valuable resource for developers wanting to learn OpenGL and graphics programming.

      View full story
    • By TheChubu
      The Khronos™ Group, an open consortium of leading hardware and software companies, announces from the SIGGRAPH 2017 Conference the immediate public availability of the OpenGL® 4.6 specification. OpenGL 4.6 integrates the functionality of numerous ARB and EXT extensions created by Khronos members AMD, Intel, and NVIDIA into core, including the capability to ingest SPIR-V™ shaders.
      SPIR-V is a Khronos-defined standard intermediate language for parallel compute and graphics, which enables content creators to simplify their shader authoring and management pipelines while providing significant source shading language flexibility. OpenGL 4.6 adds support for ingesting SPIR-V shaders to the core specification, guaranteeing that SPIR-V shaders will be widely supported by OpenGL implementations.
      OpenGL 4.6 adds the functionality of these ARB extensions to OpenGL’s core specification:
      GL_ARB_gl_spirv and GL_ARB_spirv_extensions to standardize SPIR-V support for OpenGL GL_ARB_indirect_parameters and GL_ARB_shader_draw_parameters for reducing the CPU overhead associated with rendering batches of geometry GL_ARB_pipeline_statistics_query and GL_ARB_transform_feedback_overflow_querystandardize OpenGL support for features available in Direct3D GL_ARB_texture_filter_anisotropic (based on GL_EXT_texture_filter_anisotropic) brings previously IP encumbered functionality into OpenGL to improve the visual quality of textured scenes GL_ARB_polygon_offset_clamp (based on GL_EXT_polygon_offset_clamp) suppresses a common visual artifact known as a “light leak” associated with rendering shadows GL_ARB_shader_atomic_counter_ops and GL_ARB_shader_group_vote add shader intrinsics supported by all desktop vendors to improve functionality and performance GL_KHR_no_error reduces driver overhead by allowing the application to indicate that it expects error-free operation so errors need not be generated In addition to the above features being added to OpenGL 4.6, the following are being released as extensions:
      GL_KHR_parallel_shader_compile allows applications to launch multiple shader compile threads to improve shader compile throughput WGL_ARB_create_context_no_error and GXL_ARB_create_context_no_error allow no error contexts to be created with WGL or GLX that support the GL_KHR_no_error extension “I’m proud to announce OpenGL 4.6 as the most feature-rich version of OpenGL yet. We've brought together the most popular, widely-supported extensions into a new core specification to give OpenGL developers and end users an improved baseline feature set. This includes resolving previous intellectual property roadblocks to bringing anisotropic texture filtering and polygon offset clamping into the core specification to enable widespread implementation and usage,” said Piers Daniell, chair of the OpenGL Working Group at Khronos. “The OpenGL working group will continue to respond to market needs and work with GPU vendors to ensure OpenGL remains a viable and evolving graphics API for all its customers and users across many vital industries.“
      The OpenGL 4.6 specification can be found at https://khronos.org/registry/OpenGL/index_gl.php. The GLSL to SPIR-V compiler glslang has been updated with GLSL 4.60 support, and can be found at https://github.com/KhronosGroup/glslang.
      Sophisticated graphics applications will also benefit from a set of newly released extensions for both OpenGL and OpenGL ES to enable interoperability with Vulkan and Direct3D. These extensions are named:
      GL_EXT_memory_object GL_EXT_memory_object_fd GL_EXT_memory_object_win32 GL_EXT_semaphore GL_EXT_semaphore_fd GL_EXT_semaphore_win32 GL_EXT_win32_keyed_mutex They can be found at: https://khronos.org/registry/OpenGL/index_gl.php
      Industry Support for OpenGL 4.6
      “With OpenGL 4.6 our customers have an improved set of core features available on our full range of OpenGL 4.x capable GPUs. These features provide improved rendering quality, performance and functionality. As the graphics industry’s most popular API, we fully support OpenGL and will continue to work closely with the Khronos Group on the development of new OpenGL specifications and extensions for our customers. NVIDIA has released beta OpenGL 4.6 drivers today at https://developer.nvidia.com/opengl-driver so developers can use these new features right away,” said Bob Pette, vice president, Professional Graphics at NVIDIA.
      "OpenGL 4.6 will be the first OpenGL release where conformant open source implementations based on the Mesa project will be deliverable in a reasonable timeframe after release. The open sourcing of the OpenGL conformance test suite and ongoing work between Khronos and X.org will also allow for non-vendor led open source implementations to achieve conformance in the near future," said David Airlie, senior principal engineer at Red Hat, and developer on Mesa/X.org projects.

      View full story
    • By _OskaR
      Hi,
      I have an OpenGL application but without possibility to wite own shaders.
      I need to perform small VS modification - is possible to do it in an alternative way? Do we have apps or driver modifictions which will catch the shader sent to GPU and override it?
    • By xhcao
      Does sync be needed to read texture content after access texture image in compute shader?
      My simple code is as below,
      glUseProgram(program.get());
      glBindImageTexture(0, texture[0], 0, GL_FALSE, 3, GL_READ_ONLY, GL_R32UI);
      glBindImageTexture(1, texture[1], 0, GL_FALSE, 4, GL_WRITE_ONLY, GL_R32UI);
      glDispatchCompute(1, 1, 1);
      // Does sync be needed here?
      glUseProgram(0);
      glBindFramebuffer(GL_READ_FRAMEBUFFER, framebuffer);
      glFramebufferTexture2D(GL_READ_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
                                     GL_TEXTURE_CUBE_MAP_POSITIVE_X + face, texture[1], 0);
      glReadPixels(0, 0, kWidth, kHeight, GL_RED_INTEGER, GL_UNSIGNED_INT, outputValues);
       
      Compute shader is very simple, imageLoad content from texture[0], and imageStore content to texture[1]. Does need to sync after dispatchCompute?
  • Advertisement