• Advertisement
Sign in to follow this  

OpenGL Scissors Rendering problems

This topic is 3790 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 am struggling with a OpenGL scissors problem. My source code is below. I am trying to draw a 2 dimensional rectangular display with three independent sqaure scissor sections inside the rectangle. Thus I am using the glScissor function to do this. Within each sqaure is a bitmap that I am rotating. All of this works on my PC. But as soon as I run the code on any other PC, my problems start: The first scissor section is perfect, but the other two are scrambled...the rendering has gone wrong (purple stripes) Has any one got an idea what it could be? Is it a OpenGL driver issue? A video screen card issue? Or something in my code? Thanx! GLint width,height; float ratio; width = (OpenGLAPPanelCombined->Width+1)/3; height = (OpenGLAPPanelCombined->Height); ratio = (float)width/height; glEnable(GL_SCISSOR_TEST); //Set the Position glScissor(0, 0, width, height); glViewport(0, 0, width, height); glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glLoadIdentity(); // Reset The View glTranslatef(0.0f,0.0f,-5.0f); glRotatef(pSensorVectorCalc->roll[SpotSampleNr],0.0f,0.0f,1.0f); glBindTexture(GL_TEXTURE_2D, texture[0]); glBegin(GL_QUADS); // Front Face glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.8f, -1.8f, 0.0f); glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.8f, -1.8f, 0.0f); glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.8f, 1.8f, 0.0f); glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.8f, 1.8f, 0.0f); // Back Face glEnd(); zrot[0]+= 1.0f; EditDispRoll->Text = IntToStr((int)pSensorVectorCalc->roll[SpotSampleNr]); glDisable(GL_SCISSOR_TEST); //Set the Position glEnable(GL_SCISSOR_TEST); glScissor(width, 0, width, height); glViewport(width, 0, width, height); glLoadIdentity(); // Reset The View glTranslatef(0.0f,0.0f,-5.0f); glRotatef(pSensorVectorCalc->pitch[SpotSampleNr],0.0f,0.0f,1.0f); glBindTexture(GL_TEXTURE_2D, texture[1]); glBegin(GL_QUADS); // Front Face glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.8f, -1.8f, 0.0f); glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.8f, -1.8f, 0.0f); glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.8f, 1.8f, 0.0f); glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.8f, 1.8f, 0.0f); // Back Face glEnd(); zrot[1]+= 1.0f; EditDispPitch->Text = IntToStr((int)pSensorVectorCalc->pitch[SpotSampleNr]); glDisable(GL_SCISSOR_TEST); //Set the Position glEnable(GL_SCISSOR_TEST); glScissor(width*2, 0, width, height); glViewport(width*2, 0, width, height); glLoadIdentity(); // Reset The View glTranslatef(0.0f,0.0f,-5.0f); glRotatef(-1*pSensorVectorCalc->yaw[SpotSampleNr],0.0f,0.0f,1.0f); glBindTexture(GL_TEXTURE_2D, texture[2]); glBegin(GL_QUADS); // Front Face glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.8f, -1.8f, 0.0f); glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.8f, -1.8f, 0.0f); glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.8f, 1.8f, 0.0f); glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.8f, 1.8f, 0.0f); // Back Face glEnd(); glDisable(GL_SCISSOR_TEST); zrot[2]+=-1.0f; EditDispYaw->Text = IntToStr((int)pSensorVectorCalc->yaw[SpotSampleNr]);

Share this post


Link to post
Share on other sites
Advertisement
One thing I see is that your Clear command will only affect the first part of your rendering. Clear is only done in the scissored part. You should clear before enabling scissor test or set the scissor rect to the whole area.

You could clear each viewport, but it will probably be slower.

Share this post


Link to post
Share on other sites
Hi Zongo

Thanx for the input! I have tried to clear the screen and depth buffer before I enabled the scissor test as you said but it did not work. Could it not be a screen card issue? Does all screen cards support the scissoring method? How could I test for that?

Thanx for the help

Share this post


Link to post
Share on other sites
Scissoring is some basic operation of the GPU and exists since OpenGL 1.0 I think and should be supported everywhere, so it's most probably that something else conflicts with it.

Make sure you don't leak a state from one frame to another, you may want to disable scissoring just before your Clear.

ColorMask/DephtMask also influence Clear (they are set as TRUE by default, so if you did not touch them, it's not the problem).

I do not see anything from your snippet otherwise.

Share this post


Link to post
Share on other sites
Ok sorry my fault...the problem is solved. glClear wasn't called before the scissor test as I thought. Now that it is called first, it works!!!

Thanx again for the help!

Share this post


Link to post
Share on other sites
Sign in to follow this  

  • Advertisement
  • Advertisement
  • Popular Tags

  • Advertisement
  • Popular Now

  • Similar Content

    • By QQemka
      Hello. I am coding a small thingy in my spare time. All i want to achieve is to load a heightmap (as the lowest possible walking terrain), some static meshes (elements of the environment) and a dynamic character (meaning i can move, collide with heightmap/static meshes and hold a varying item in a hand ). Got a bunch of questions, or rather problems i can't find solution to myself. Nearly all are deal with graphics/gpu, not the coding part. My c++ is on high enough level.
      Let's go:
      Heightmap - i obviously want it to be textured, size is hardcoded to 256x256 squares. I can't have one huge texture stretched over entire terrain cause every pixel would be enormous. Thats why i decided to use 2 specified textures. First will be a tileset consisting of 16 square tiles (u v range from 0 to 0.25 for first tile and so on) and second a 256x256 buffer with 0-15 value representing index of the tile from tileset for every heigtmap square. Problem is, how do i blend the edges nicely and make some computationally cheap changes so its not obvious there are only 16 tiles? Is it possible to generate such terrain with some existing program?
      Collisions - i want to use bounding sphere and aabb. But should i store them for a model or entity instance? Meaning i have 20 same trees spawned using the same tree model, but every entity got its own transformation (position, scale etc). Storing collision component per instance grats faster access + is precalculated and transformed (takes additional memory, but who cares?), so i stick with this, right? What should i do if object is dynamically rotated? The aabb is no longer aligned and calculating per vertex min/max everytime object rotates/scales is pretty expensive, right?
      Drawing aabb - problem similar to above (storing aabb data per instance or model). This time in my opinion per model is enough since every instance also does not have own vertex buffer but uses the shared one (so 20 trees share reference to one tree model). So rendering aabb is about taking the model's aabb, transforming with instance matrix and voila. What about aabb vertex buffer (this is more of a cosmetic question, just curious, bumped onto it in time of writing this). Is it better to make it as 8 points and index buffer (12 lines), or only 2 vertices with min/max x/y/z and having the shaders dynamically generate 6 other vertices and draw the box? Or maybe there should be just ONE 1x1x1 cube box template moved/scaled per entity?
      What if one model got a diffuse texture and a normal map, and other has only diffuse? Should i pass some bool flag to shader with that info, or just assume that my game supports only diffuse maps without fancy stuff?
      There were several more but i forgot/solved them at time of writing
      Thanks in advance
    • By RenanRR
      Hi All,
      I'm reading the tutorials from learnOpengl site (nice site) and I'm having a question on the camera (https://learnopengl.com/Getting-started/Camera).
      I always saw the camera being manipulated with the lookat, but in tutorial I saw the camera being changed through the MVP arrays, which do not seem to be camera, but rather the scene that changes:
      Vertex Shader:
      #version 330 core layout (location = 0) in vec3 aPos; layout (location = 1) in vec2 aTexCoord; out vec2 TexCoord; uniform mat4 model; uniform mat4 view; uniform mat4 projection; void main() { gl_Position = projection * view * model * vec4(aPos, 1.0f); TexCoord = vec2(aTexCoord.x, aTexCoord.y); } then, the matrix manipulated:
      ..... glm::mat4 projection = glm::perspective(glm::radians(fov), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f); ourShader.setMat4("projection", projection); .... glm::mat4 view = glm::lookAt(cameraPos, cameraPos + cameraFront, cameraUp); ourShader.setMat4("view", view); .... model = glm::rotate(model, glm::radians(angle), glm::vec3(1.0f, 0.3f, 0.5f)); ourShader.setMat4("model", model);  
      So, some doubts:
      - Why use it like that?
      - Is it okay to manipulate the camera that way?
      -in this way, are not the vertex's positions that changes instead of the camera?
      - I need to pass MVP to all shaders of object in my scenes ?
       
      What it seems, is that the camera stands still and the scenery that changes...
      it's right?
       
       
      Thank you
       
    • By dpadam450
      Sampling a floating point texture where the alpha channel holds 4-bytes of packed data into the float. I don't know how to cast the raw memory to treat it as an integer so I can perform bit-shifting operations.

      int rgbValue = int(textureSample.w);//4 bytes of data packed as color
      // algorithm might not be correct and endianness might need switching.
      vec3 extractedData = vec3(  rgbValue & 0xFF000000,  (rgbValue << 8) & 0xFF000000, (rgbValue << 16) & 0xFF000000);
      extractedData /= 255.0f;
    • By Devashish Khandelwal
      While writing a simple renderer using OpenGL, I faced an issue with the glGetUniformLocation function. For some reason, the location is coming to be -1.
      Anyone has any idea .. what should I do?
    • By Andrey OGL_D3D
      Hi all!
      I try to use the Sun shafts effects via post process in my 3DEngine, but i have some artefacts on final image(Please see attached images).
      The effect contains the following passes:
      1) Depth scene pass;
      2) "Shafts pass" Using DepthPass Texture + RGBA BackBuffer texture.
      3) Shafts pass texture +  RGBA BackBuffer texture.
      Shafts shader for 2 pass:
      // uniform sampler2D FullSampler; // RGBA Back Buffer uniform sampler2D DepthSampler; varying vec2 tex; #ifndef saturate float saturate(float val) {     return clamp(val, 0.0, 1.0); } #endif void main(void) {     vec2 uv = tex;     float sceneDepth = texture2D(DepthSampler, uv.xy).r;     vec4  scene        = texture2D(FullSampler, tex);     float fShaftsMask     = (1.0 - sceneDepth);     gl_FragColor = vec4( scene.xyz * saturate(sceneDepth), fShaftsMask ); } final shader:
      // uniform sampler2D FullSampler; // RGBA Back Buffer uniform sampler2D BlurSampler; // shafts sampler varying vec4 Sun_pos; const vec4    ShaftParams = vec4(0.1,2.0,0.1,2.0); varying vec2 Tex_UV; #ifndef saturate  float saturate(float val) {     return clamp(val, 0.0, 1.0); } #endif vec4 blendSoftLight(vec4 a, vec4 b) {   vec4 c = 2.0 * a * b + a * a * (1.0 - 2.0 * b);   vec4 d = sqrt(a) * (2.0 * b - 1.0) + 2.0 * a * (1.0 - b);       // TODO: To look in Crysis what it the shit???   //return ( b < 0.5 )? c : d;   return any(lessThan(b, vec4(0.5,0.5,0.5,0.5)))? c : d; } void main(void) {     vec4 sun_pos = Sun_pos;     vec2    sunPosProj = sun_pos.xy;     //float    sign = sun_pos.w;     float    sign = 1.0;     vec2    sunVec = sunPosProj.xy - (Tex_UV.xy - vec2(0.5, 0.5));     float    sunDist = saturate(sign) * saturate( 1.0 - saturate(length(sunVec) * ShaftParams.y ));     sunVec *= ShaftParams.x * sign;     vec4 accum;     vec2 tc = Tex_UV.xy;     tc += sunVec;     accum = texture2D(BlurSampler, tc);     tc += sunVec;     accum += texture2D(BlurSampler, tc) * 0.875;     tc += sunVec;     accum += texture2D(BlurSampler, tc) * 0.75;     tc += sunVec;     accum += texture2D(BlurSampler, tc) * 0.625;     tc += sunVec;     accum += texture2D(BlurSampler, tc) * 0.5;     tc += sunVec;     accum += texture2D(BlurSampler, tc) * 0.375;     tc += sunVec;     accum += texture2D(BlurSampler, tc) * 0.25;     tc += sunVec;     accum += texture2D(BlurSampler, tc) * 0.125;     accum  *= 0.25 * vec4(sunDist, sunDist, sunDist, 1.0);           accum.w += 1.0 - saturate(saturate(sign * 0.1 + 0.9));     vec4    cScreen = texture2D(FullSampler, Tex_UV.xy);           vec4    cSunShafts = accum;     float fShaftsMask = saturate(1.00001 - cSunShafts.w) * ShaftParams.z * 2.0;              float fBlend = cSunShafts.w;     vec4 sunColor = vec4(0.9, 0.8, 0.6, 1.0);     accum =  cScreen + cSunShafts.xyzz * ShaftParams.w * sunColor * (1.0 - cScreen);     accum = blendSoftLight(accum, sunColor * fShaftsMask * 0.5 + 0.5);     gl_FragColor = accum; } Demo project:
      Demo Project
      Shaders for postprocess Shaders/SunShaft/
      What i do wrong ?
      Thanks!
       


  • Advertisement