From 31f19438c73b207f506ba0b1187d2de75c166a5b Mon Sep 17 00:00:00 2001
From: Luke Lau <luke_lau@icloud.com>
Date: Thu, 9 Apr 2020 17:39:54 +0100
Subject: [PATCH] Fix blending

---
 billboardfrag.glsl | 20 +++++++++++++++++++-
 clouds.cpp         | 42 +++++++++++++++---------------------------
 2 files changed, 34 insertions(+), 28 deletions(-)

diff --git a/billboardfrag.glsl b/billboardfrag.glsl
index 840ec89..2349e4d 100644
--- a/billboardfrag.glsl
+++ b/billboardfrag.glsl
@@ -3,7 +3,25 @@ uniform vec4 color;
 uniform sampler2D tex;
 in vec2 texCoord;
 out vec4 FragColor;
+uniform bool modulate;
 void main() {
-  FragColor = texture(tex, texCoord).r * color;
+	// Cf = color from fragment, Ct = color from texture
+	// Cc = color from texture environment(?) assume to be 0?
+	// Af = alpha from fragment, At = alpha from texture
+	// C = output color, A = output alpha
+	float f = texture(tex, texCoord).r;
+	if (modulate) { 
+		// GL_MODULATE: C
+		// C = Cf * Ct
+		// A = Af * At				
+		FragColor = color * f;
+	} else {
+		// GL_BLEND:
+		// C = Cf * (1-Ct) + Cc * Ct
+		// A = Af * At
+		vec3 C = color.rgb * (1 - f);
+		float A = color.a * f;
+		FragColor = vec4(C, A);
+	}
 }
 
diff --git a/clouds.cpp b/clouds.cpp
index 7bb51e8..96612e8 100644
--- a/clouds.cpp
+++ b/clouds.cpp
@@ -84,21 +84,21 @@ void calculateMetaballs() {}
 #define NQ 1
 GLuint bbTexIds[NQ];
 
+// Stores attenuation ratio inside r channel
+// Should be highest value at center
 void precalculateBillboardTextures() {
   float data[32 * 32];
   // TODO: properly calculate this instead of whatever this is
   for (int j = 0; j < 32; j++)
     for (int i = 0; i < 32; i++)
-      data[i + j * 32] = fmin(1.f, 0.1f + 2.f * (distance(vec2(i, j), vec2(16, 16)) / 16));
+      data[i + j * 32] = fmin(1.f, 0.3f + 2.f * (distance(vec2(i, j), vec2(16, 16)) / 16));
 
   glGenTextures(NQ, bbTexIds);
 
-  /* GLuint captureFBO; */
-  /* glGenFramebuffers(1, &captureFBO); */
   for (int i = 0; i < NQ; i++) {
     glBindTexture(GL_TEXTURE_2D, bbTexIds[i]);
-    /* glTexImage2D(GL_TEXTURE_2D, 0, GL_R32F, 32, 32, 0, GL_RED, */
-    /*              GL_FLOAT, data); */
+    checkError();
+
     glTexImage2D(GL_TEXTURE_2D, 0, GL_RED, 32, 32, 0, GL_RED, GL_FLOAT, data);
     glGenerateMipmap(GL_TEXTURE_2D); // required, otherwise texture is blank
 
@@ -152,6 +152,7 @@ void shadeClouds() {
   bbColors.clear();
 
   glDisable(GL_DEPTH_TEST);
+  // shaderOutput * 0 + buffer * shader alpha
   glBlendFunc(GL_ZERO, GL_SRC_ALPHA);
   glEnable(GL_BLEND);
 
@@ -159,24 +160,11 @@ void shadeClouds() {
   sort(metaballs.begin(), metaballs.end(), [](Metaball &a, Metaball &b) {
     return distance(sunPos, a.pos) < distance(sunPos, b.pos);
   });
-  /* GLuint fbo; */
-  /* glGenFramebuffers(1, &fbo); */
-  /* glBindFramebuffer(GL_FRAMEBUFFER, fbo); */
-  /* glBindTexture(GL_TEXTURE_2D, attenuationTex); */
-  /* glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, */
-  /*              GL_UNSIGNED_BYTE, NULL); */
-  /* glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, */
-  /*                        attenuationTex, 0); */
-  /* assert(glCheckFramebufferStatus(GL_FRAMEBUFFER) == GL_FRAMEBUFFER_COMPLETE); */
 
   glActiveTexture(GL_TEXTURE0);
   glBindTexture(GL_TEXTURE_2D, bbTexIds[0]);
   glUniform1i(glGetUniformLocation(bbProg, "tex"), 0);
 
-/*   glClearColor(1, 1, 1, 1); */
-/*   glClear(GL_COLOR_BUFFER_BIT); */
-
-
   GLuint modelLoc = glGetUniformLocation(bbProg, "model");
 
   for (auto k : metaballs) {
@@ -195,8 +183,9 @@ void shadeClouds() {
 
     // Map the billboard texture with GL_MODULATE.
     // i.e. multiply rather than add
-    // TODO: FIX- this crashes with invalid operation
-    /* glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE); */
+    // but glTexEnv is for the old fixed function pipeline --
+    // need to just tell our fragment shader then to modulate
+    glUniform1i(glGetUniformLocation(bbProg, "modulate"), 1);
 
     // Render the billboard.
     glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
@@ -215,16 +204,11 @@ void shadeClouds() {
     pixel *= sunColor;
 
     // Store the color into an array C[k] as the color of the billboard.
-    fprintf(stderr, "pixel: ");
-    dump(pixel);
     bbColors.push_back(pixel);
   }
 
-  /* saveFBO(); */
+  saveFBO();
   checkError();
-
-  /* glDeleteFramebuffers(1, &fbo); */
-  /* glBindFramebuffer(GL_FRAMEBUFFER, 0); // render to screen */
 }
 
 void renderObject() {}
@@ -237,6 +221,7 @@ void renderClouds() {
 
   glDisable(GL_DEPTH_TEST);
   glEnable(GL_BLEND);
+  // shaderOutput * 1 + buffer * shader alpha
   glBlendFunc(GL_ONE, GL_SRC_ALPHA);
   for (int i = 0; i < metaballs.size(); i++) {
     Metaball k = metaballs[i];
@@ -253,7 +238,7 @@ void renderClouds() {
     // Set the billboard color as C[n].
     fprintf(stderr, "bbColors[i]: ");
     dump(bbColors[i]);
-    /* bbColors[i] = {0,0,0,0.5}; */
+    bbColors[i].w = 1;
     glUniform4fv(glGetUniformLocation(bbProg, "color"), 1,
                  glm::value_ptr(bbColors[i]));
 
@@ -262,6 +247,9 @@ void renderClouds() {
     glBindTexture(GL_TEXTURE_2D, bbTexIds[0]);
     glUniform1i(glGetUniformLocation(bbProg, "tex"), 0);
 
+    // Don't modulate it -- blend it
+    glUniform1i(glGetUniformLocation(bbProg, "modulate"), 0);
+
     // Render the billboard with the blending function.
     glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
   }
-- 
2.30.2