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


OpenGL OpenGL 2D quads don't render right

Recommended Posts

krogoth    122
As a part of my engine, I want to load fonts from files in a custom format where each character is stored as a greyscale image and render them as 2D quads with textures. To show the text, I want to set a color and then have the texture go from that color when the pixel is white to transparent - the greyscale image should be the alpha channel and the RGB should be set to whatever I want. When I try out the code, everything renders real nice, and all the characters are in the right place and have the right size, but each quad that should hold a character is either green (my color) or black, depending on the code I''m using. Does anyone know what could be doing this? In case it helps, I explain my code and how I know the data is right below. I start the OpenGL initialization with this code: glClearColor( 0.0f, 0.0f, 0.0f, 1.0f ); glEnable( GL_CULL_FACE ); glCullFace( GL_BACK ); glDepthFunc( GL_LESS ); glEnable( GL_DEPTH_TEST ); glEnable( GL_LINE_SMOOTH ); glEnable( GL_POINT_SMOOTH ); glEnable( GL_POLYGON_SMOOTH ); glEnable( GL_BLEND ); glBlendFunc( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA ); glEnable( GL_TEXTURE_2D ); glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR ); glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT ); glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT ); Then, before rendering the text, I do: glMatrixMode( GL_PROJECTION ); glPushMatrix( ); glLoadIdentity( ); glOrtho( 0.0f, (GLfloat)(vid_screenWidth), 0.0f, (GLfloat)(vid_screenHeight), -1.0f, 1.0f ); glMatrixMode( GL_MODELVIEW ); glPushMatrix( ); glLoadIdentity( ); glDisable( GL_DEPTH_TEST ); glDisable( GL_CULL_FACE ); vid_screenHeight and vid_screenWidth are the resolution of the window. I start the text rendering with a few things that could be put in other places: glPixelStorei( GL_UNPACK_ALIGNMENT, 1 ); glPushAttrib( GL_PIXEL_MODE_BIT ); And then I have this, which should set the color of the pixels but doesn''t do anything (color is an array of floats): glPixelTransferf( GL_RED_BIAS, color[0] ); glPixelTransferf( GL_GREEN_BIAS, color[1] ); glPixelTransferf( GL_BLUE_BIAS, color[2] ); For each character, I do this (where font->data[cc] is the : glBegin( GL_QUADS ); glTexImage2D( GL_TEXTURE_2D, 0, 1, font->fullWidths[cc], font->fullHeight, 0, GL_RGB GL_UNSIGNED_BYTE, font->data[cc] ); glColor3f( color[0], color[1], color[2] ); color[1] -= 0.15f; #define TEXTURE( x, y ) glTexCoord2f( x, y ); printf( "Texture at %f %f\n", x, y ) #define VERTEX( x, y ) glVertex2f( x, y ); printf( "Vertex out at %i, %i\n", x, y ) TEXTURE( 0.0f, 0.0f ); VERTEX( deltaX, y ); TEXTURE( xfar, 0.0f ); VERTEX( font->widths[cc] + deltaX, y ); TEXTURE( xfar, yfar ); VERTEX( font->widths[cc] + deltaX, y - font->fontHeight ); TEXTURE( 0.0f, yfar ); VERTEX( deltaX, y - font->fontHeight ); glEnd( ); deltaX += font->widths[cc] + font->charSpacing; xfar and yfar are the texture coordinates of the corners of the text and deltaX is the left position of the character. fullWidth and fullHeight are the dimensions the character is stored at (multiples of two), and I use xfar and yfar to set the actual dimensions of the character. And after I''m done, I do this: glPopAttrib( ); // in another function... glEnable( GL_CULL_FACE ); glEnable( GL_DEPTH_TEST ); glMatrixMode( GL_PROJECTION ); glPopMatrix( ); glMatrixMode( GL_MODELVIEW ); glPopMatrix( ); I have some debugging output in addition to what is shown above, so for the ''!'' character, I get this (including an ASCII art rendering with each pixel as blank for black and 1-9 showing the intensity): Character !: | | 46 | 69 | 69 | 68 | 46 | 36 | 12 | 992 | 571 | | | | | | ----| Used color 0.000000, 0.100000, 0.000000 Texture at 0.000000 0.000000 Vertex out at 51, 476 Texture at 0.750000 0.000000 Vertex out at 54, 476 Texture at 0.750000 0.812500 Vertex out at 54, 463 Texture at 0.000000 0.812500 Vertex out at 51, 463 Here you see the character image is 4 pixels wide and 16 tall (powers of two), and it shows the texture and vertex co-ordinates used. You can see the best-case output (green squares instead of black) at As you can see, the quads have the perfect position and size, but the wrong texture.

Share this post

Link to post
Share on other sites
krogoth    122
Two small problems... the ASCII art didn''t render the spaces, and I forgot to say that the format I use for glTexture2D is GL_ALPHA, not GL_RGB.

Share this post

Link to post
Share on other sites
TerranFury    142
Not an answer to your question, but a hint to make your life easier on the forums: Begin source code with [ source ] and end with [ / source ] but without the spaces.

Share this post

Link to post
Share on other sites
Derilect101    122
Could be caused by the blending. You might try using .tga files also since they can be 32 bit 24 bits color and 8 grayscale for transparency its really easy to do if you have photoshop once you have that I would use glEnable(GL_ALPHA_TEST); and then glAlphaFunc(GL_GREATER, 0.1f); this will make any black on the grayscale transparent and anything other then black transparent how it is now it sounds like the colors from the background of your tiles are blending with the scenery color. Hope this helps if ya need more help just say so

Share this post

Link to post
Share on other sites

  • Partner Spotlight

  • Similar Content

    • By pseudomarvin
      I assumed that if a shader is computationally expensive then the execution is just slower. But running the following GLSL FS instead just crashes
      void main() { float x = 0; float y = 0; int sum = 0; for (float x = 0; x < 10; x += 0.00005) { for (float y = 0; y < 10; y += 0.00005) { sum++; } } fragColor = vec4(1, 1, 1 , 1.0); } with unhandled exception in nvoglv32.dll. Are there any hard limits on the number of steps/time that a shader can take before it is shut down? I was thinking about implementing some time intensive computation in shaders where it would take on the order of seconds to compute a frame, is that possible? Thanks.
    • By Arulbabu Donbosco
      There are studios selling applications which is just copying any 3Dgraphic content and regenerating into another new window. especially for CAVE Virtual reality experience. so that the user opens REvite or CAD or any other 3D applications and opens a model. then when the user selects the rendered window the VR application copies the 3D model information from the OpenGL window. 
      I got the clue that the VR application replaces the windows opengl32.dll file. how this is possible ... how can we copy the 3d content from the current OpenGL window.
      anyone, please help me .. how to go further... to create an application like VR CAVE. 
    • By cebugdev
      hi all,

      i am trying to build an OpenGL 2D GUI system, (yeah yeah, i know i should not be re inventing the wheel, but this is for educational and some other purpose only),
      i have built GUI system before using 2D systems such as that of HTML/JS canvas, but in 2D system, i can directly match a mouse coordinates to the actual graphic coordinates with additional computation for screen size/ratio/scale ofcourse.
      now i want to port it to OpenGL, i know that to render a 2D object in OpenGL we specify coordiantes in Clip space or use the orthographic projection, now heres what i need help about.
      1. what is the right way of rendering the GUI? is it thru drawing in clip space or switching to ortho projection?
      2. from screen coordinates (top left is 0,0 nd bottom right is width height), how can i map the mouse coordinates to OpenGL 2D so that mouse events such as button click works? In consideration ofcourse to the current screen/size dimension.
      3. when let say if the screen size/dimension is different, how to handle this? in my previous javascript 2D engine using canvas, i just have my working coordinates and then just perform the bitblk or copying my working canvas to screen canvas and scale the mouse coordinates from there, in OpenGL how to work on a multiple screen sizes (more like an OpenGL ES question).
      lastly, if you guys know any books, resources, links or tutorials that handle or discuss this, i found one with marekknows opengl game engine website but its not free,
      Just let me know. Did not have any luck finding resource in google for writing our own OpenGL GUI framework.
      IF there are no any available online, just let me know, what things do i need to look into for OpenGL and i will study them one by one to make it work.
      thank you, and looking forward to positive replies.
    • By fllwr0491
      I have a few beginner questions about tesselation that I really have no clue.
      The opengl wiki doesn't seem to talk anything about the details.
      What is the relationship between TCS layout out and TES layout in?
      How does the tesselator know how control points are organized?
          e.g. If TES input requests triangles, but TCS can output N vertices.
             What happens in this case?
      In this article,
      the isoline example TCS out=4, but TES in=isoline.
      And gl_TessCoord is only a single one.
      So which ones are the control points?
      How are tesselator building primitives?
    • By Orella
      I've been developing a 2D Engine using SFML + ImGui.
      Here you can see an image
      The editor is rendered using ImGui and the scene window is a sf::RenderTexture where I draw the GameObjects and then is converted to ImGui::Image to render it in the editor.
      Now I need to create a 3D Engine during this year in my Bachelor Degree but using SDL2 + ImGui and I want to recreate what I did with the 2D Engine. 
      I've managed to render the editor like I did in the 2D Engine using this example that comes with ImGui. 
      3D Editor preview
      But I don't know how to create an equivalent of sf::RenderTexture in SDL2, so I can draw the 3D scene there and convert it to ImGui::Image to show it in the editor.
      If you can provide code will be better. And if you want me to provide any specific code tell me.
  • Popular Now