OpenGL floating point texture experiment

floating_point_experiment.m

void floatTextureExperiment
{
    GLenum err = 0;
    GLuint texture1;
    glGenTextures(1, &texture1);
    glActiveTexture(GL_TEXTURE1);
    glBindTexture(GL_TEXTURE_2D, texture1);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    GLuint texture2;
    glGenTextures(1, &texture2);
    glActiveTexture(GL_TEXTURE2);
    glBindTexture(GL_TEXTURE_2D, texture2);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    GLuint frameBuffer;
    glGenFramebuffers(1, &frameBuffer);
    glBindFramebuffer(GL_FRAMEBUFFER, frameBuffer);
    
    char* bgVShaderStr =
    "attribute vec4 vPosition;\n"
    "attribute vec2 in_texCoord;\n"
    "varying vec2 texCoord;\n"
    "void main(){\n"
    "  texCoord = in_texCoord;\n"
    "  gl_Position = vPosition;\n"
    "}\n";
    char* bgFShaderStr =
    "uniform sampler2D tex;\n"
    "varying highp vec2 texCoord;\n"
    "void main(){\n"
    "  highp vec4 color = texture2D(tex, texCoord);\n"
    "  //gl_FragColor = vec4(color.r+1.0/256.0, 1.0, 0.0, 1.0);\n"
    "  gl_FragColor = vec4(color.r/2.0, 1.0, 0.0, 1.0);\n"
    "}\n";
    GLuint program = esLoadProgram(bgVShaderStr, bgFShaderStr);

    int width = 2;
    int height = 2;
    
//    uint8_t buf[] = {20, 0, 0, 255,
//        100, 0, 0, 255,
//        180, 0, 0, 255,
//        255, 0, 0, 255};
//    glActiveTexture(GL_TEXTURE1);
//    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, buf);
    float buf[] = {0.2, 0.0, 0.0, 1.0,
        0.8, 0.0, 0.0, 1.0,
        1.6, 0.0, 0.0, 1.0,
        1.9, 0.0, 0.0, 1.0};
    hfloat* hfbuf = (hfloat*)malloc(16 * sizeof(hfloat));
    for (int i = 0; i < 16; i++) {
        hfbuf[i] = convertFloatToHFloat(buf+i);
    }
    glActiveTexture(GL_TEXTURE1);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_HALF_FLOAT_OES, hfbuf);
    free(hfbuf);
    
    glUseProgram(program);
    static const GLfloat imageVertices[] = {
        -1.0f, -1.0f,
        1.0f, -1.0f,
        -1.0f,  1.0f,
        1.0f,  1.0f,
    };
    GLint attribLoc = glGetAttribLocation(program, "vPosition");
    glVertexAttribPointer(attribLoc, 2, GL_FLOAT, GL_FALSE, 0, imageVertices);
    static const GLfloat noRotationTextureCoordinates[] = {
        0.0f, 0.0f,
        1.0f, 0.0f,
        0.0f, 1.0f,
        1.0f, 1.0f,
    };
    attribLoc = glGetAttribLocation(program, "in_texCoord");
    glVertexAttribPointer(attribLoc, 2, GL_FLOAT, GL_FALSE, 0, noRotationTextureCoordinates);
    glViewport(0, 0, width, height);
    
    glActiveTexture(GL_TEXTURE2);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, 0);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture2, 0);
    GLenum frameBufferStatus = glCheckFramebufferStatus(GL_FRAMEBUFFER);
    if (frameBufferStatus != GL_FRAMEBUFFER_COMPLETE) {
        printf("Incomplete framebuffer: %d\n", frameBufferStatus - GL_FRAMEBUFFER_COMPLETE);
        printFrameBufferStatus();
    }
    
    int texLoc = glGetUniformLocation(program, "tex");
    glUniform1i(texLoc, GL_TEXTURE1 - GL_TEXTURE0);
    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
    
    uint8_t* m = (uint8_t*)malloc(4 * 4 * sizeof(uint8_t));
    memset(m, 0, 4 * 4 * sizeof(uint8_t));
    glReadPixels(0, 0, 2, 2, GL_RGBA, GL_UNSIGNED_BYTE, m);
    for (int i = 0; i < 4; i++) {
        for (int j = 0; j < 4; j++) {
            printf("%d, ", m[4*i+j]);
        }
        printf("\n");
    }
    free(m);
}

void printFrameBufferStatus()
{
    if (frameBufferStatus == GL_FRAMEBUFFER_INCOMPLETE_ATTACHMENT) {
        printf("GL_FRAMEBUFFER_INCOMPLETE_ATTACHMENT\n");
    } else if (frameBufferStatus == GL_FRAMEBUFFER_INCOMPLETE_DIMENSIONS) {
        printf("GL_FRAMEBUFFER_INCOMPLETE_DIMENSIONS\n");
    } else if (frameBufferStatus == GL_FRAMEBUFFER_INCOMPLETE_MISSING_ATTACHMENT) {
        printf("GL_FRAMEBUFFER_INCOMPLETE_MISSING_ATTACHMENT\n");
    } else if (frameBufferStatus == GL_FRAMEBUFFER_UNSUPPORTED) {
        printf("GL_FRAMEBUFFER_UNSUPPORTED\n");
    } else {
        printf("Unknown status!\n");
    }
}