Bdtjtk

With my water render, I am having an issue, where based on the camera position and orientation, there is a "flicker" effect/problem on the terrain in the game. Basically, a gray overlay "flickers" onto the terrain, but then disappears. This repeats as the camera position/orientation is changed.

Specifically, it happens on only specific terrain "islands" and near the part of the terrain which intersects the water quad.

So, to illustrate the issue:

Water with no flicker

Water with flicker; In the bottom right hand side of the image, there is a slight gray overlay on the "small" island that protrudes from the main island.

Additionally, here is an animated .gif demonstrating the issue:

As a final note, this flickering does not happen, say, for the large body of terrain in the background.

Could anyone please let me know what additional details I need to provide, as well as point me in the right direction as to the problem and possible resolution?

Thank you in advance!

Below is my process of mapping the reflection to the water quad:

I first created one frame buffer object upon program start up:
Framebuffer Object Creation:

// FBO objct

unsigned int framebuffer;

glGenFramebuffers(1, &framebuffer);

glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);



// generate texture

unsigned int texColorBuffer;

glGenTextures(1, &texColorBuffer);

glBindTexture(GL_TEXTURE_2D, texColorBuffer);

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 1024, 768, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

glBindTexture(GL_TEXTURE_2D, 0);



// attach it to currently bound framebuffer object

glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texColorBuffer, 0);



unsigned int rbo;

glGenRenderbuffers(1, &rbo);

glBindRenderbuffer(GL_RENDERBUFFER, rbo);

glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH24_STENCIL8, 1024, 768);

glBindRenderbuffer(GL_RENDERBUFFER, 0);



glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT, GL_RENDERBUFFER, rbo);



if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)

    std::cout << "ERROR::FRAMEBUFFER:: Framebuffer is not complete!" << std::endl;

glBindFramebuffer(GL_FRAMEBUFFER, 0);

I created a single water quad:

// real_offsets needed for instancing

std::vector<glm::vec2> real_offsets;

real_offsets.push_back(glm::vec2(650, 450));

glm::mat4 waterQuad = glm::mat4(1.0f);

        waterQuad = translate(waterQuad, vec3(0, 480.0, 0));

        waterQuad = scale(waterQuad, vec3(100, 1, 100));

        objects.push_back(std::shared_ptr <Object>(new Object("waterpane_very_low.obj", waterQuad, real_offsets, true, false

            , glm::vec3(0.0, 0.5, 1.0))));

Then in the main game loop, I used the frame buffer object to save a snapshot of the scene:
Main Game Loop:

do {

    glEnable(GL_CLIP_DISTANCE0);



    // Use frame buffer object

    glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);



    // Clear the screen

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);



    // Draw scene with no water quad to FBO

    // [...]



    // Disable frame buffer object

    glBindFramebuffer(GL_FRAMEBUFFER, 0);



    // Save frame buffer object texture to texture unit 0 to use later

    glActiveTexture(GL_TEXTURE0);

    glBindTexture(GL_TEXTURE_2D, texColorBuffer);



    glDisable(GL_CLIP_DISTANCE0);



    // Clear the screen

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);



    // Draw whole scene, including water quad as normal

    // [...]



    // Swap buffers

    glfwSwapBuffers(window);

    glfwPollEvents();



} while (glfwGetKey(window, GLFW_KEY_ESCAPE) != GLFW_PRESS && glfwWindowShouldClose(window) == 0);

In my normal object's shader, I enabled a clip plane to control what is drawn to the reflection texture: NormalObjects.vertexshader:

const vec4 plane = vec4(0,1,0,-480);

gl_ClipDistance[0] = dot( M * vec4(vertex,1), plane);

gl_Position =  MVP * vec4(vertex,1);

In my water.vertexshader, I performed necessary calculations to transform a local vertex: water.vertexshader:

// MVP_offset = P * V * M_offset, where M_offset depends on a vector of vecs2 passed in containing instancing offsets

        clipSpace =  MVP_offset * vec4(vertex,1.0);

        gl_Position = MVP_offset * vec4(vertex,1.0);    // instanced vertex

Then in my water.fragmentshader, I applied Blinn-Phong shading and sampled the reflection texture and projectively mapped it: water.fragmentshader:

// Sampler variable

uniform sampler2D waterTexture;



// Projectively map the reflection texture

vec2 clipProj = (clipSpace.xy / clipSpace.w) / 2.0 + 0.5;

clipProj.y *= -1.0f; // flip texture around



// waterTexture was assigned texture unit 0

vec4 finalVec = vec4(texture(waterTexture, clipProj).rgb, 1.0);



vec4 finalVec2 = finalVec * vec4(ambientComponent() + diffuseComponent(modelNormal,lightVec) + specularComponent(modelNormal, lightVec), 1.0);



FragColor = finalVec2;